Answer (Detailed Solution Below) – Option 2 : Tricalcium Silicate Free MPSC AE CE Mains 2019 Official (Paper 1) 100 Questions 200 Marks 120 Mins The setting and hardening of cement after addition of water is due to hydration of some of the constituent compounds of cement such as Tricalcium aluminate, Tricalcium silicate, Dicalcium silicate, and Tetra calcium aluminoferrite.
These compounds are known as Bogue’s Compounds. Tricalcium aluminate (C 3 A): Celite is the quickest one to react when the water is added to the cement. It is responsible for the flash setting. The increase of this content will help in the manufacture of Quick Setting Cement. The heat of hydration is 865 J/Cal,
Tricalcium silicate (C 3 S): This is also called as Alite, This is also responsible for the early strength of the concrete. The cement that has more C 3 S content is good for cold weather concreting. The heat of hydration is 500 J/Cal, Dicalcium Silicate (C 2 S): This compound will undergo reaction slowly.
It is responsible for the progressive strength of concrete. This is also called as Belite, The heat of hydration is 260 J/Cal. Tetra calcium Alumino ferrite (C 4 AF): This is called as Felite, It has the poorest cementing value but it responsible for long term gain of strength of the cement. The heat of hydration is 420 J/Cal,
Hence the component in cement which has the property of hydrating rapidly and is responsible to provide not only early strength but also the ultimate strength is Tricalcium silicate (C 3 S) Last updated on Oct 11, 2022 The Maharashtra Public Service Commission (MPSC) has released new notification for MPSC AE Recruitment.
A total number of 151 vacancies are released for Civil, Mechanical and Electrical desciplines. Application process is started on 3rd October 2022 and the candidates can apply till 23rd October 2022. There are 3 stages of selection process – Prelims, Mains and Interview. The prelims exam is scheduled on 17th December 2022.
The candidates who will get qualified in the prelims are eligible to attend the mains. The final select list will be released after the Interview.
- 1 Which compound imparts long term strength to cement?
- 1.1 Which of the following is responsible for strength?
- 1.2 Which cement compound has the greatest influence on the long term strength development of concrete?
- 2 Which of the following compounds of cement helps in high early strength gain?
- 2.1 Which three of the following are long term benefits of strength training?
- 2.2 Which compound is responsible for 14 to 28 days of strength in cement?
- 3 What is responsible for the early strength?
Which component is responsible for strength in cement?
Silica is responsible for strength of cement, alumina imparts quick setting property, Calcium Sulphate delays setting of cement, Magnesium Oxide in large quantity-causes delayed expansion.
Which compound imparts long term strength to cement?
Dicalcium Silicate is about (25 – 40 %) of cement. It hydrates and hardens slowly and takes a long time to add to the strength (after a year or more). It imparts resistance to chemical attack.
Which compound is responsible for long duration strength?
Di-calcium silicate (C 2 S) is the last compound that is formed after the addition of water in the cement which may require a year or so for its formation. It is responsible for the progressive strength of cement. The structures in which strength is required in later stages, proportion of C 2 S is increased.
Which constituents of cement contributes to early strength and which to long term strength?
What is in This Stuff? The importance of concrete in modern society cannot be overestimated. Look around you and you will find concrete structures everywhere such as buildings, roads, bridges, and dams. There is no escaping the impact concrete makes on your everyday life.
So what is it? Concrete is a composite material which is made up of a filler and a binder. The binder (cement paste) “glues” the filler together to form a synthetic conglomerate. The constituents used for the binder are cement and water, while the filler can be fine or coarse aggregate. The role of these constituents will be discussed in this section.
Cement, as it is commonly known, is a mixture of compounds made by burning limestone and clay together at very high temperatures ranging from 1400 to 1600 ]C. Although there are other cements for special purposes, this module will focus solely on portland cement and its properties.
The production of portland cement begins with the quarrying of limestone, CaCO 3, Huge crushers break the blasted limestone into small pieces. The crushed limestone is then mixed with clay (or shale), sand, and iron ore and ground together to form a homogeneous powder. However, this powder is microscopically heterogeneous.
(See flowchart.) Figure 1: A flow diagram of Portland Cement production. The mixture is heated in kilns that are long rotating steel cylinders on an incline. The kilns may be up to 6 meters in diameter and 180 meters in length. The mixture of raw materials enters at the high end of the cylinder and slowly moves along the length of the kiln due to the constant rotation and inclination. Figure 2: Schematic diagram of rotary kiln. As the mixture moves down the cylinder, it progresses through four stages of transformation. Initially, any free water in the powder is lost by evaporation. Next, decomposition occurs from the loss of bound water and carbon dioxide.
This is called calcination, The third stage is called clinkering. During this stage, the calcium silicates are formed. The final stage is the cooling stage. The marble-sized pieces produced by the kiln are referred to as clinker, Clinker is actually a mixture of four compounds which will be discussed later.
The clinker is cooled, ground, and mixed with a small amount of gypsum (which regulates setting) to produce the general-purpose portland cement. Water is the key ingredient, which when mixed with cement, forms a paste that binds the aggregate together.
- The water causes the hardening of concrete through a process called hydration.
- Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydrates or hydration products.
- Details of the hydration process are explored in the next section.
- The water needs to be pure in order to prevent side reactions from occurring which may weaken the concrete or otherwise interfere with the hydration process.
The role of water is important because the water to cement ratio is the most critical factor in the production of “perfect” concrete. Too much water reduces concrete strength, while too little will make the concrete unworkable. Concrete needs to be workable so that it may be consolidated and shaped into different forms (i.e.
Walls, domes, etc.). Because concrete must be both strong and workable, a careful balance of the cement to water ratio is required when making concrete. Aggregates are chemically inert, solid bodies held together by the cement. Aggregates come in various shapes, sizes, and materials ranging from fine particles of sand to large, coarse rocks.
Because cement is the most expensive ingredient in making concrete, it is desirable to minimize the amount of cement used.70 to 80% of the volume of concrete is aggregate keeping the cost of the concrete low. The selection of an aggregate is determined, in part, by the desired characteristics of the concrete.
For example, the density of concrete is determined by the density of the aggregate. Soft, porous aggregates can result in weak concrete with low wear resistance, while using hard aggregates can make strong concrete with a high resistance to abrasion. Aggregates should be clean, hard, and strong. The aggregate is usually washed to remove any dust, silt, clay, organic matter, or other impurities that would interfere with the bonding reaction with the cement paste.
It is then separated into various sizes by passing the material through a series of screens with different size openings. Refer to Demonstration 1 Table 1: Classes of Aggregates
|class||examples of aggregates used||uses|
|ultra-lightweight||vermiculite ceramic spheres perlite||lightweight concrete which can be sawed or nailed, also for its insulating properties|
|lightweight||expanded clay shale or slate crushed brick||used primarily for making lightweight concrete for structures, also used for its insulating properties.|
|normal weight||crushed limestone sand river gravel crushed recycled concrete||used for normal concrete projects|
|heavyweight||steel or iron shot steel or iron pellets||used for making high density concrete for shielding against nuclear radiation|
Refer to Demonstration 2 The choice of aggregate is determined by the proposed use of the concrete. Normally sand, gravel, and crushed stone are used as aggregates to make concrete. The aggregate should be well-graded to improve packing efficiency and minimize the amount of cement paste needed.
Also, this makes the concrete more workable. Refer to Demonstration 3 Properties of Concrete Concrete has many properties that make it a popular construction material. The correct proportion of ingredients, placement, and curing are needed in order for these properties to be optimal. Good-quality concrete has many advantages that add to its popularity.
First, it is economical when ingredients are readily available. Concrete’s long life and relatively low maintenance requirements increase its economic benefits. Concrete is not as likely to rot, corrode, or decay as other building materials. Concrete has the ability to be molded or cast into almost any desired shape.
Building of the molds and casting can occur on the work-site which reduces costs. Concrete is a non-combustible material which makes it fire-safe and able withstand high temperatures. It is resistant to wind, water, rodents, and insects. Hence, concrete is often used for storm shelters. Concrete does have some limitations despite its numerous advantages.
Concrete has a relatively low tensile strength (compared to other building materials), low ductility, low strength-to-weight ratio, and is susceptible to cracking. Concrete remains the material of choice for many applications regardless of these limitations.
- Hydration of Portland Cement Concrete is prepared by mixing cement, water, and aggregate together to make a workable paste.
- It is molded or placed as desired, consolidated, and then left to harden.
- Concrete does not need to dry out in order to harden as commonly thought.
- The concrete (or specifically, the cement in it) needs moisture to hydrate and cure (harden).
When concrete dries, it actually stops getting stronger. Concrete with too little water may be dry but is not fully reacted. The properties of such a concrete would be less than that of a wet concrete. The reaction of water with the cement in concrete is extremely important to its properties and reactions may continue for many years.
|Cement Compound||Weight Percentage||Chemical Formula|
|Tricalcium silicate||50 %||Ca 3 SiO 5 or 3CaO, SiO 2|
|Dicalcium silicate||25 %||Ca 2 SiO 4 or 2CaO, SiO 2|
|Tricalcium aluminate||10 %||Ca 3 Al 2 O 6 or 3CaO, Al 2 O 3|
|Tetracalcium aluminoferrite||10 %||Ca 4 Al 2 Fe 2 O 10 or 4CaO, Al 2 O 3, Fe 2 O 3|
|Gypsum||5 %||CaSO 4,2H 2 O|
Table 2: Composition of portland cement with chemical composition and weight percent. When water is added to cement, each of the compounds undergoes hydration and contributes to the final concrete product. Only the calcium silicates contribute to strength. Tricalcium silicate is responsible for most of the early strength (first 7 days). Dicalcium silicate, which reacts more slowly, contributes only to the strength at later times. Tricalcium silicate will be discussed in the greatest detail. The equation for the hydration of tricalcium silicate is given by: Tricalcium silicate + Water->Calcium silicate hydrate+Calcium hydroxide + heat 2 Ca 3 SiO 5 + 7 H 2 O -> 3 CaO,2SiO 2,4H 2 O + 3 Ca(OH) 2 + 173.6kJ Upon the addition of water, tricalcium silicate rapidly reacts to release calcium ions, hydroxide ions, and a large amount of heat. The pH quickly rises to over 12 because of the release of alkaline hydroxide (OH – ) ions. This initial hydrolysis slows down quickly after it starts resulting in a decrease in heat evolved. The reaction slowly continues producing calcium and hydroxide ions until the system becomes saturated. Once this occurs, the calcium hydroxide starts to crystallize. Simultaneously, calcium silicate hydrate begins to form. Ions precipitate out of solution accelerating the reaction of tricalcium silicate to calcium and hydroxide ions. (Le Chatlier’s principle). The evolution of heat is then dramatically increased. The formation of the calcium hydroxide and calcium silicate hydrate crystals provide “seeds” upon which more calcium silicate hydrate can form. The calcium silicate hydrate crystals grow thicker making it more difficult for water molecules to reach the unhydrated tricalcium silicate. The speed of the reaction is now controlled by the rate at which water molecules diffuse through the calcium silicate hydrate coating. This coating thickens over time causing the production of calcium silicate hydrate to become slower and slower. Figure 3: Schematic illustration of the pores in calcium silicate through different stages of hydration. The above diagrams represent the formation of pores as calcium silicate hydrate is formed. Note in diagram (a) that hydration has not yet occurred and the pores (empty spaces between grains) are filled with water. Diagram (b) represents the beginning of hydration. In diagram (c), the hydration continues. Although empty spaces still exist, they are filled with water and calcium hydroxide. Diagram (d) shows nearly hardened cement paste. Note that the majority of space is filled with calcium silicate hydrate. That which is not filled with the hardened hydrate is primarily calcium hydroxide solution. The hydration will continue as long as water is present and there are still unhydrated compounds in the cement paste. Dicalcium silicate also affects the strength of concrete through its hydration. Dicalcium silicate reacts with water in a similar manner compared to tricalcium silicate, but much more slowly. The heat released is less than that by the hydration of tricalcium silicate because the dicalcium silicate is much less reactive. The products from the hydration of dicalcium silicate are the same as those for tricalcium silicate: Dicalcium silicate + Water->Calcium silicate hydrate + Calcium hydroxide +heat 2 Ca 2 SiO 4 + 5 H 2 O-> 3 CaO,2SiO 2,4H 2 O + Ca(OH) 2 + 58.6 kJ The other major components of portland cement, tricalcium aluminate and tetracalcium aluminoferrite also react with water. Their hydration chemistry is more complicated as they involve reactions with the gypsum as well. Because these reactions do not contribute significantly to strength, they will be neglected in this discussion. Although we have treated the hydration of each cement compound independently, this is not completely accurate. The rate of hydration of a compound may be affected by varying the concentration of another. In general, the rates of hydration during the first few days ranked from fastest to slowest are: tricalcium aluminate > tricalcium silicate > tetracalcium aluminoferrite > dicalcium silicate. Refer to Demonstration 4 Heat is evolved with cement hydration. This is due to the breaking and making of chemical bonds during hydration. The heat generated is shown below as a function of time. Figure 4: Rate of heat evolution during the hydration of portland cement The stage I hydrolysis of the cement compounds occurs rapidly with a temperature increase of several degrees. Stage II is known as the dormancy period. The evolution of heat slows dramatically in this stage.
The dormancy period can last from one to three hours. During this period, the concrete is in a plastic state which allows the concrete to be transported and placed without any major difficulty. This is particularly important for the construction trade who must transport concrete to the job site. It is at the end of this stage that initial setting begins.
In stages III and IV, the concrete starts to harden and the heat evolution increases due primarily to the hydration of tricalcium silicate. Stage V is reached after 36 hours. The slow formation of hydrate products occurs and continues as long as water and unhydrated silicates are present.
- Refer to Demonstration 5 Strength of Concrete The strength of concrete is very much dependent upon the hydration reaction just discussed.
- Water plays a critical role, particularly the amount used.
- The strength of concrete increases when less water is used to make concrete.
- The hydration reaction itself consumes a specific amount of water.
Concrete is actually mixed with more water than is needed for the hydration reactions. This extra water is added to give concrete sufficient workability. Flowing concrete is desired to achieve proper filling and composition of the forms, The water not consumed in the hydration reaction will remain in the microstructure pore space. Figure 5: Schematic drawings to demonstrate the relationship between the water/cement ratio and porosity. The empty space (porosity) is determined by the water to cement ratio. The relationship between the water to cement ratio and strength is shown in the graph that follows. Figure 6: A plot of concrete strength as a function of the water to cement ratio. Low water to cement ratio leads to high strength but low workability. High water to cement ratio leads to low strength, but good workability. The physical characteristics of aggregates are shape, texture, and size.
- These can indirectly affect strength because they affect the workability of the concrete.
- If the aggregate makes the concrete unworkable, the contractor is likely to add more water which will weaken the concrete by increasing the water to cement mass ratio.
- Time is also an important factor in determining concrete strength.
Concrete hardens as time passes. Why? Remember the hydration reactions get slower and slower as the tricalcium silicate hydrate forms. It takes a great deal of time (even years!) for all of the bonds to form which determine concrete’s strength. It is common to use a 28-day test to determine the relative strength of concrete.
- Concrete’s strength may also be affected by the addition of admixtures.
- Admixtures are substances other than the key ingredients or reinforcements which are added during the mixing process.
- Some admixtures add fluidity to concrete while requiring less water to be used.
- An example of an admixture which affects strength is superplasticizer.
This makes concrete more workable or fluid without adding excess water. A list of some other admixtures and their functions is given below. Note that not all admixtures increase concrete strength. The selection and use of an admixture are based on the need of the concrete user.
|AIR ENTRAINING||improves durability, workability, reduces bleeding, reduces freezing/thawing problems (e.g. special detergents)|
|SUPERPLASTICIZERS||increase strength by decreasing water needed for workable concrete (e.g. special polymers)|
|RETARDING||delays setting time, more long term strength, offsets adverse high temp. weather (e.g. sugar )|
|ACCELERATING||speeds setting time, more early strength, offsets adverse low temp. weather (e.g. calcium chloride)|
|MINERAL ADMIXTURES||improves workability, plasticity, strength (e.g. fly ash)|
|PIGMENT||adds color (e.g. metal oxides)|
Table 3: A table of admixtures and their functions. Durability is a very important concern in using concrete for a given application. Concrete provides good performance through the service life of the structure when concrete is mixed properly and care is taken in curing it.
- Good concrete can have an infinite life span under the right conditions.
- Water, although important for concrete hydration and hardening, can also play a role in decreased durability once the structure is built.
- This is because water can transport harmful chemicals to the interior of the concrete leading to various forms of deterioration.
Such deterioration ultimately adds costs due to maintenance and repair of the concrete structure. The contractor should be able to account for environmental factors and produce a durable concrete structure if these factors are considered when building concrete structures.
Which of the following is responsible for strength?
Lime : It imparts strength and soundness to content.
Which cement compound has the greatest influence on the long term strength development of concrete?
Long-term strength development of concrete in arid conditions , August–October 2001, Pages 363-373 The strength of concrete is traditionally characterized by the 28-day value. However, strength of concrete is expected to increase with time at a continuously diminishing rate. Knowledge of the strength-time relationship is of importance when a structure is subjected to a certain type of loading at a later age,
Many factors can significantly influence the compressive strength of concrete. These include cement type, w/c ratio, aggregate content, water curing period, and exposure conditions. Water/cement ratio affects the rate of gain in strength and it has been reported that as mixes with low w/c ratios gain strength more rapidly than mixes with higher w/c ratios,
Washa and Wendt presented results for concrete made with high early strength Portland cement where the strength at 50 years was 2.4 times the 28-day strength. Another study by Walz showed that the 30-year strength of ordinary Portland cement (OPC) concrete was 2.3 times the 28-day strength while that of Portland blast furnace slag cement concrete was 3.1 times the 28-day strength.
Washa and Wendt have also reported that concretes reach their peak strength between 10 and 25 years and thereafter undergo some retrogression of strength while Lange showed that air-cured concretes had about 35% higher strength at three years than that at 28 days. An earlier study by Gonnerman and Lerch using a concrete mix with a w/c ratio of 0.49 reported that OPC concrete resulted in a gain in strength of 27.5% (over the 28-day strength) in 5 years, while the sulphate resisting Portland cement concrete had a lower 28-day strength, and the gain in strength was 56% over the same period.
The compressive strength of concrete made with sulphate resisting cement was about 75–90% of the strength of concrete made with ordinary Portland cement after five years. Soroka and Baum showed that continuously wet specimens increased 20% in strength above those of the the uncured specimens, over 90 days.
Also, the 28-day strength of concrete cubes subjected to continuously wet curing was about 40% more than the strength of the corresponding uncured cubes. Carette et al. reported compressive strength results for a period up to 2 years. Non-silica-fume concretes exhibited an ascending compressive strength during the testing period, while the silica-fume concretes exhibited a plateau or a small decrease in the compressive strength after one year.
Aitcin presented results on seven field concretes exposed for periods ranging from 4 to 6 years. Non-silica-fume concretes showed more gain in strength (23–40% in 2 years and 50% in 6 years) than silica-fume concretes (−12% to +29% in 2 years and −31% to +17% in 6 years).
Also, in contrast to OPC concrete, which develops the bulk of its ultimate strength by 28 days, the strength development of concrete containing pulverized fuel ash (PFA) not only continues for much longer but varies both with the PFA used and age, Proper curing is more important to the compressive strength development of PFA concrete.
Long-term investigations on the effects of natural environmental conditions of the middle east on concrete properties, in particular the compressive strength are rare. However, a long-term investigation (up to 1300 days) was reported by Fattuhi earlier.
The results showed that at early ages the compressive strength of concrete continuously cured in a humidity chamber was slightly lower than that of similar concrete cured under atmospheric conditions. However, this situation was reversed when the concrete cubes were exoposed for more than 1200 days. This highlights the importance of conducting long-term tests.
Nevertheless, the above work indicated that the compressive strength of concrete subjected to middle east weather conditions continued to increase with time. Concrete strengths can also be significantly influenced by other factors such as carbonation, and in turn, the rate of carbonation is also influenced by mix constituents and the curing regime,,
In this study various parameters affecting the compressive strength are presented. Short- and long-term gains in strength are discussed. Concrete cubes with various constituents were made, and their strengths were measured up to an age of 1800 days while subjected to the arid environmental conditions of Kuwait.
The weather in Kuwait is characterized by hot dry periods and the summers usually extend over several months (Fig.1). Winters are mild with low amounts of rain fall. The majority of the specimens were made with OPC. White and sulphate resisting cements were also used.
Typical fineness for the ordinary, white and sulphate resisting Portland cements used were 349, 392 and 349 m 2 /kg. The fine and coarse aggregates (see Table 1) consisted of natural desert sand and crushed desert limestone gravel. Twelve admixtures were used in various mixes. Table 2 presents composition and recommended dosages of these admixtures.
Forty-seven concrete mixes were made and the At 28 days of age, the cubes were exposed to the atmospheric conditions of Kuwait by placing them on the roof of the laboratory building. Hence the cubes were subjected to sun radiation, higher and more fluctuating temperatures, and possibly higher concentrations of air pollutants.
The sun radiation, and higher and more fluctuating atmospheric temperatures, can affect the concrete in two ways. Aggregate and cement paste have different coefficients of thermal expansion, and the contraction and Three Portland cements were used: ordinary (mix E), white (mix W) and sulphate-resisting (mix R).
The results showed (see Fig.2) that the 28-days average compressive strength was highest for the white cement concrete (53.8 MPa), followed closely by the OPC concrete (52.2 MPa). However, the sulphate-resisting Portland cement concrete had an average compressive strength value of 46.0 MPa at 28 days.
- All specimens continued to gain strength with time.
- Specimens made with white cement had an Mix A had a cement content of 435 kg/m 3, while mix M had a cement content of 460 kg/m 3 (see Table 3).
- Concrete specimens A1 and M1 were water cured for 6 days while specimens A2 and M2 were water cured for 27 days after demoulding.
Fig.3 shows the compressive strength results for the four sets of concrete specimens A and M. It can be seen that by increasing the water curing period from 6 to 27 days, higher compressive strengths were obtained at all ages. The differences in the compressive The w/c ratios for concretes K, E, E1, E2 and E3 ranged from 0.45 to 0.80.
The results (Fig.4) showed that as the w/c ratio increased there was a significant decrease in the compressive strength. The 28-day compressive strength for the concrete with a w/c ratio of 0.45 (mix K) was 56.0 MPa, while that for concrete with a w/c ratio of 0.60 (mix E1) was only 38.7 MPa. Although concretes with w/c=0.6 and above have not been recommended in Kuwait since the eighties, such concretes have been used Various types of admixtures were used to make concrete mixes S1–S9 and the workabilities of these mixes as measured by the slump test, varied between 8 and 70 mm.
The maximum difference in the compressive strength at 28 and 1800 days for the various admixtures was about 16% (see Fig.5). The gain in strength at 1800 days over the 28-days value ranged from 18% to 28%. The highest compressive strength at 28 days was that for a concrete (mix S5), containing an admixture A ̄ 6 (retarder based on Concrete specimens N1–N5 were water cured for periods ranging from 0 to 27 days.
These specimens contained admixture A ̄ 2, At 28 days, increasing the water-curing period from 0 (mix N5) to 27 days (mix N1) resulted in an increase of 51% in the compressive strength (see Fig.7). However, this difference in strength was almost halved by initially water curing for 2 days only. At 1800 days, the advantage of increasing the water curing period from 0 to 27 days was only about 7%.
This clearly Three curing compounds/aids were used; C ̄ 1 based on sodium silicate, C ̄ 2 based on resin and C ̄ 3 based on wax emulsion. These compounds were used in concrete specimens C1, C2 and C3, respectively. Specimens C2 and C3 showed slightly higher compressive strengths than specimens C1 (see Fig.9).
- However, the maximum difference between the compressive strengths of the concretes brushed with either one of the three curing compounds throughout the testing period was about 9%.
- Fig.7, Fig.9 show that Concrete specimens K, E, E1, E2 and E3 were cast during the summer.
- However, concrete specimens O, P, Q, V and Z were similar but were cast during the winter period.
These specimens had w/c ratios ranging from 0.45 to 0.80. Results of concrete specimens cast during the winter period (see Fig.10) show similar trends to those cast during the summer. As the w/c ratio was increased, the compressive strength decreased as expected.
- However, the compressive strengths were higher for concrete specimens Fig.11 shows the compressive strength results for concrete specimens H1–H6.
- The water binder ratio (w/b) for mixes H4 and H5 was 0.45 and for the other mixes it was 0.5.
- At 28 days, concrete specimens H4 which had silica fume replacing 10% of sand by weight and with a cement content of 410 kg/m 3, achieved the highest compressive strength of 70.3 MPa, followed by concrete specimens H2 at 61.1 MPa which contained more silica fume and less cement.
Concrete specimens H4, H5 and H6 had a similar 1. Concretes made with white Portland cement showed the highest compressive strength values, followed by ordinary Portland cement and sulphate resisting Portland cement. The average gain in strength (above the 28-day values) over 1800 days for the three types of concrete was 33% (ranged from 29% to 36%).2.
- The compressive strength of the concrete decreased significantly as the w/c ratio increased as expected.
- The higher the w/c ratio, the higher was the gain in strength with age above the 28-day The research presented in this paper was funded by the Environmental Protection Council (Kuwait), through a grant to Kuwait University.
Thanks to Mr.K. Hijab, for his assistance during the preparation of specimens and the initial testing process and to Messrs.M. Abou Naja and M. Morelli for their assistance during the latter part of the investigation.
N.I Fattuhi P.C Aitcin et al. British Standards Institution. BS 1881: part 116: Methods for determination of compressive strength of concrete cubes. Carette GG, Malhotra VM, Aitcin PC. Preliminary data on long-term strength development on condensed silica-fume. Dhir RK, Hubbard FH, Munday JG, Jones MR, Duerden SL. Contribution of PFA to concrete workability and strength. Fattuhi NI. Influence of Kuwaiti atmospheric conditions on the development of compressive strength for concrete. N.I Fattuhi
There are more references available in the full text version of this article.
Chloride-induced rebar corrosion is the dominant threat to reinforced concrete durability, whereas its effect mechanism and damage degree are quite variable in different marine exposure zones. Accordingly, a concrete beam was prepared and exposed to marine fields across various corrosion zones for 7 years, and its durability performance (especially rebar corrosion and chloride ion profiles) was evaluated. The results show that the most corroded zone occurred in the high tide level of the tidal zone, and a chloride convection zone of 4 mm emerged concomitantly. Moreover, the rebars were characterized as vertical nonuniform corrosion and localized corrosion, and their corrosion products mainly comprised two outer and inner layers. Therefore, better corrosion protection should be applied to concrete in the tidal zone, when the concrete structure is simultaneously exposed to different corrosion zones. However, the negative impact of long-term marine exposure on the mechanical properties and carbonation resistance of concrete is negligible. In addition, many marine organisms (barnacles and oysters) were found to be subregionally attached to the surface of concrete located in the submerged and tidal zones. Furthermore, they can protect the concrete by forming the shielding layer, delaying the permeation of chloride ions. After ten years of marine exposure, chloride and calcium profiles and petrographic data were obtained from the tidal and submerged zones of six concrete panels differing in binder composition. Moisture and portlandite profiles were also determined on the submerged concrete. The data enables us to improve our understanding of the impact of sea water exposure and can also be used for service life modeling. The depth of the maximum chloride content and the depth of the microstructurally changed zone were comparable. Both depths progressed over time and reached a depth of as much as 10 mm after ten years of exposure. When using these and other field data for testing of chloride ingress prediction models, we recommend excluding datapoints from the microstructurally changed zone, i.e., the outermost datapoints including the maximum chloride content, unless reactive transport models are used. While there is extensive data now available for the performance of crumb rubber concrete (CRC) in laboratory mixes, it is essential to understand whether satisfactory performance can be replicated in real-world structures. This is particularly the case for the area of residential construction, which is a sector that is sometimes characterised by fairly average outcomes due to a sometimes-low skilled workforce operating with minimal supervision. To replicate a real-world situation, CRC research has been moved from “the lab to the slab” in this paper. Two large-scale (4 × 8 m each) reinforced concrete residential footing slabs were constructed. One was cast with CRC and the other with a standard residential mix of conventional concrete (CC). In addition, two reinforced concrete residential ground slabs of different dimensions were constructed out of CRC and CC mixes to assess abrasion resistance. These ground slabs were poured in high traffic entrances of a civil engineering laboratory. All mixes were provided by a commercial ready-mix company and the construction was undertaken by an experienced footing contractor. A large range of factors have been investigated and compared. Those related to construction requirements, included the effect of using rubber on concrete mixing, delivery, workability, pumpability, ease of surface finishing, and curing. The contractors reported easy screeding and less physical effort to do so, with no difference reported when finishing the concrete surface when using a concrete power trowel for footing slabs. Other factors that were investigated included: fresh and hardened density, compressive strength, modulus of elasticity, shrinkage, carbonation, chloride ingress, abrasion resistance, rising damp, and corrosion. The results show that CRC is a potentially viable and promising alternative to conventional concrete in the residential concrete market. With the world facing a huge shortage of water and labourer, the use of curing compounds in place of conventional and prolonged wet curing is inevitable. However, hot weather conditions and the quality control issues in many countries necessitate diligence in the selection of curing compounds. However, the ASTM standard (water loss test) – the only standard method available – exhibits large variability in results and cannot be used to reliably assess the effectiveness and qualify curing compounds. Also, the compressive strength test is not sensitive enough to assess the quality of curing compounds. Given this scenario, there is a need for an alternate test method to assess the effectiveness of curing compounds. This paper presents an experimental investigation on the suitability of tests on various durability parameters to assess the effectiveness of curing compounds. The oxygen permeability index (OPI), water sorptivity index (WSI), non-steady-state migration coefficient for chloride penetration (D nssm ), total porosity, and compressive strength were used as test parameters. These parameters of mortar specimens prepared using Ordinary Portland Cement and cured using wet curing, air drying, and five curing compounds were evaluated. The mortar specimens were kept in the following two controlled environments: (i) mild (25 °C, 65% RH) and (ii) hot (45 °C, 55% RH). The study found that the OPI, WSI, and D nssm are suitable and more sensitive than the compressive strength in assessing the effectiveness of curing compounds. Amongst these three, OPI test showed more consistent results and can be recommended as a test for qualifying curing compounds. The results of an experimental study to evaluate the residual compressive and shear strengths of novel coconut-fibre-reinforced-concrete (CFRC) interlocking blocks are discussed in this paper. This work is part of a research project in which the development of mortar-free interlocking structures is intended for cheap and easy-to-built earthquake-resistant housing. Recently, mortar-free walls made of these blocks were tested under a series of harmonic and earthquake loadings. Only few blocks at the wall bottom were damaged, the other blocks (with no visual damage) had gone under numerous uplifts which might have affected the block strengths. In parallel, the blocks without any use over a period of time in tropical environment are also considered as coconut fibres are natural materials whose strengths might have decayed. These two cases represent two real scenarios in which (I) a structure stands without having an earthquake over a period and (II) a structure having a series of dynamic loading. In both cases, the residual strengths are of much interest to determine the remaining serviceable life of the structures. The results show that the impact of dynamic load histories on capacities of CFRC interlocking blocks was relatively more in comparison to the effect of age. The compressive and in-plane strengths were increased up to 3.2% and 5.7%, respectively, after undergoing a series of dynamic loading. This shows the advantage of earthquake loading on mortar-free structures. The objective of this work is experimental characterisation and numerical modelling of coupled behaviours between drying shrinkage and plastic damage in concrete. In the first part, we present an original experimental study on an ordinary concrete in order to determine material damage induced by drying shrinkage. Uniaxial compression tests are performed on samples dried for different periods. It is shown that material damage can be caused by drying process. Mechanical behaviour becomes more brittle with higher damage kinetics when concrete is dried. In the second part, a constitutive model is proposed in order to describe coupled hydro-mechanical behaviour of partially saturated concrete. This model takes into account induced damage, mechanical and capillary plastic deformations. Numerical simulations of experimental tests are presented, and show a qualitatively good agreement with experimental data. The results are relevant with respect to the importance of drying process in the durability study of concrete structures.
A shear strength estimation model for reinforced concrete (RC) beams, the so-called dual potential capacity model (DPCM), has previously been proposed by the authors. In this study, the DPCM is extended to estimate the shear strength of RC beams strengthened in shear by using externally-bonded fiber-reinforced polymer (FRP) composites. The proposed model has been derived so as to take into account the effects of the type of FRP composite, fiber-bonding configuration, and fiber layout, and it can also determine the critical shear failure modes of RC beams strengthened by externally-bonded FRP composites. To verify the accuracy of the proposed model, shear test results of 227 RC beams strengthened by externally-bonded FRP composites were collected from previous studies, and it is shown that the analysis results estimated by the DPCM agree well with those test results. The structural evaluation of existing concrete structures is becoming everyday more important for several reasons ranging from their seismic assessment to the presence of increased design loads, from the damage caused by fire to forensic investigations and so on. Whilst it is generally recognized that concrete coring provides the most reliable information on concrete strength, it should also be mentioned that this kind of test is responsible of slight damage to the structure and that it can be carried out only for structural elements with sufficient spacing between the reinforcing bars. Thus, it would be highly desirable to obtain reliable information by means of non-destructive techniques (NDT). One of the major drawbacks of the well-known combined method SonReb is the effect of the carbonation on the rebound number. In this paper two correction formulas for this index based on the thickness of the carbonated concrete cover and, to a smaller extent, on the strength of the concrete itself, are proposed. The formulas have been determined by means of finite elements modeling (FEM) of the impact between the plunger of a Schmidt hammer and the concrete surface. Results from FEM have shown a good agreement with experimental results. The proposed correction formulas can provide a more reliable concrete strength evaluation without significantly increasing the cost and the time for the experimental tests. Improvement in quality of concrete compositions can be achieved both by using chemical additives, and using local components to create a new generation of concrete, which is a highly relevant objective for concrete technology. The industrial wastes produced by the enterprises of Volgograd region are complex mineral and organic compounds having various chemical and physical properties. Among additives of the organic nature the construction acrylic paints production waste is of scientific and practical interest. It has been checked that it is possible to use an organic additive, a water-dispersible acrylic monomer (WDAM) – construction acrylic paints production waste as a modification, in the fine grain concrete, improving the basic properties of the construction composition. Studies have shown particular pattern of the modified concrete formation process, consisting of the water-repellent plasticizing effect of WDAM additives. The regularities of changes in the quality parameters of the concrete composition and the number of introduced additives are established. The relations of changing performance properties of effective concrete with modification WDAM have been confirmed by the results of experimental studies and developed regression model. The study shows that the creation and use of new modifiers is one of the actual ways to further enhance the performance of building materials, as well as evidentiates the tendency to expand the list of chemical additives with complex effect with organic waste. It is evident that the utilization of waste products and more efficient use of material resources have a proven economic effect. The nondestructive assessment of concrete strength in existing structures is a real and complex challenge. Recent research advances have been done, like the idea of conditional coring or the development of a bi-objective approach for assessing concrete variability. It will be shown here how, through the use of synthetic simulations and the analysis of uncertainty propagation in the investigation and assessment process, it is possible to (a) confirm the interest of these research results, (b) develop a consistent approach for an efficient and reliable assessment of concrete strength in existing structures. This work will be based on the definition of prescribed targets in terms of uncertainty of assessment and on the concept of risk, i.e. probability of missing the targets. Concrete compression is complex. Yet, understanding this behavior is indispensable for design. There are three main factors that affect concrete compression results: the specimen size, shape, and friction at its ends. These factors affect the observed phenomena, and they affect each other. This paper aims to review the current knowledge on concrete compression and the effect of size, shape and friction on it. Understanding their effects is essential for a safer design and more effective testing. Most of the advancements in this topic is old, with a few exceptions. So, this review highlights the gaps in knowledge, and reintroduces them once again. Concrete design codes should consider the size effect in calculations. Reducing friction is recommended to lower the strength variation. Reduced friction may also be used for testing smaller specimens more reliably. This leads to more accurate, and more economic concrete testing. The present paper provides a statistical approach to evaluate the effect of different sand types on the properties of self-compacting concrete (SCC). A mixture design modelling approach was used to highlight the effects of river sand (RS), crushed sand (CS) and dune sand (DS) as proportions in binary and ternary systems, on flowability, passing ability, segregation and mechanical strength of SCC. The responses of the derived statistical models are slump flow, v-funnel time, L-box, stability and compressive strength at 2, 7 and 28 days. The derived mathematical models make it possible to illustrate the variation of different responses in ternary contour plots with respect to the proportions of RS, CS and DS. This provides flexibility to optimize RS, CS and DS blends with tailor-made of a given property that suit particular recommendations. Results indicate that when flowability requirements are combined, proportions of DS and CS in binary or ternary systems with RS must be below 0.24 and 0.6 respectively. Moreover, it is shown that passing ability can be satisfied by using a CS proportion above 0.3 in RS–CS binary system and above 0.65 in CS–DS binary system. On other hand, proportions above 0.5 of CS in RS–CS binary system and above 0.2 of DS in RS–DS binary system are recommended to meet stability limits. Results also indicate that compressive strength at 2, 7 and 28 days increased with the increase of CS proportion and decreased with the increase of DS proportion in binary and ternary systems.
: Long-term strength development of concrete in arid conditions
What are the long term properties of concrete?
Abstract – It is now accepted that replacement of natural aggregates in concrete with recycled concrete aggregates obtained from construction and demolition waste is a promising technology to conserve natural resources and reduce the environmental impact of concrete.
This paper presents a study on long-term properties of concretes manufactured with recycled aggregates of different parent concrete strengths. A total of six batches of recycled aggregate concretes (RACs) were manufactured. Tests were undertaken to establish the long-term compressive strength, elastic modulus, splitting tensile strength, workability, drying shrinkage, and creep of each batch.
Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) characterizations were performed to explain the mechanisms behind the observed time-dependent and mechanical properties of RACs. Test parameters comprised the replacement ratio and parent concrete strength of the recycled aggregates used in the preparation of the new concrete mixes.
- The results indicate that the parent concrete strength of the recycled aggregates significantly affects the time-dependent and long-term mechanical properties of RACs.
- It is shown that concrete mixes containing lower strength recycled concrete aggregates develop lower mechanical properties and higher shrinkage strain and creep deformation compared to mixes prepared with higher strength recycled concrete aggregates.
Normal-strength RAC mixes containing higher strength recycled concrete aggregates develop slightly lower splitting tensile strength at all curing ages but similar compressive strength and elastic modulus in longer term (i.e. over 90 days) compared to those of the control mix.
Which of the following compounds of cement helps in high early strength gain?
|Ruchir said: (Jun 12, 2018)|
|Tricalcium Silicate (C3S) hardens rapidly and is largely responsible for initial set and early strength. In general, the early strength of Portland cement concrete is higher with increased percentages of C3S. Dicalcium Silicate (C2S) hardens slowly and contributes largely to strength increases at ages beyond 7 days.|
Which three of the following are long term benefits of strength training?
Use it or lose it – Lean muscle mass naturally diminishes with age. Your body fat percentage will increase over time if you don’t do anything to replace the lean muscle you lose over time. Strength training can help you preserve and enhance your muscle mass at any age. Strength training may also help you:
- Develop strong bones. By stressing your bones, strength training can increase bone density and reduce the risk of osteoporosis.
- Manage your weight. Strength training can help you manage or lose weight, and it can increase your metabolism to help you burn more calories.
- Enhance your quality of life. Strength training may enhance your quality of life and improve your ability to do everyday activities. Strength training can also protect your joints from injury. Building muscle also can contribute to better balance and may reduce your risk of falls. This can help you maintain independence as you age.
- Manage chronic conditions. Strength training can reduce the signs and symptoms of many chronic conditions, such as arthritis, back pain, obesity, heart disease, depression and diabetes.
- Sharpen your thinking skills. Some research suggests that regular strength training and aerobic exercise may help improve thinking and learning skills for older adults.
Which of the following provides ultimate strength to the cement?
Ultimate strength to cement is provided by dicalcium silicate. Tricalcium silicate (30-50%) is also known as ‘Alite’. It is responsible for the initial strength of cement.
Which compound is responsible for 14 to 28 days of strength in cement?
However, it was observed that a higher percentage of Tricalcium aluminate (C 3 A) leads to higher strength gain from 7 to 28 days of curing age.
What is the primary component of Portland cement that contributes to long term strength?
Hydration of Portland Cement Introduction Portland cement is a hydraulic cement, hence it derives its strength from chemical reactions between the cement and water. The process is known as hydration. Cement consists of the following major compounds (see composition of cement ):
Tricalcium silicate, C 3 S Dicalcium silicate, C 2 S Tricalcium aluminate, C 3 A Tetracalcium aluminoferrite, C 4 AF Gypsum, C S H 2
Chemical reactions during hydration When water is added to cement, the following series of reactions occur:
The tricalcium aluminate reacts with the gypsum in the presence of water to produce ettringite and heat:
Tricalcium aluminate + gypsum + water ® ettringite + heat C 3 A + 3C S H 2 + 26H ® C 6 AS 3 H 32, D H = 207 cal/g
Ettringite consists of long crystals that are only stable in a solution with gypsum. The compound does not contribute to the strength of the cement glue. The tricalcium silicate (alite) is hydrated to produce calcium silicate hydrates, lime and heat:
Tricalcium silicate + water ® calcium silicate hydrate + lime + heat 2C 3 S + 6H ® C 3 S 2 H 3 + 3CH, D H = 120 cal/g
The CSH has a short-networked fiber structure which contributes greatly to the initial strength of the cement glue. Once all the gypsum is used up as per reaction (i), the ettringite becomes unstable and reacts with any remaining tricalcium aluminate to form monosulfate aluminate hydrate crystals:
Tricalcium aluminate + ettringite + water ® monosulfate aluminate hydrate 2C 3 A + 3 C 6 A S 3 H 32 + 22H ® 3C 4 ASH 18,
The monosulfate crystals are only stable in a sulfate deficient solution. In the presence of sulfates, the crystals resort back into ettringite, whose crystals are two-and-a-half times the size of the monosulfate. It is this increase in size that causes cracking when cement is subjected to sulfate attack. The belite (dicalcium silicate) also hydrates to form calcium silicate hydrates and heat:
Dicalcium silicates + water ® calcium silicate hydrate + lime C 2 S + 4H ® C 3 S 2 H 3 + CH, D H = 62 cal/g
Like in reaction (ii), the calcium silicate hydrates contribute to the strength of the cement paste. This reaction generates less heat and proceeds at a slower rate, meaning that the contribution of C 2 S to the strength of the cement paste will be slow initially.
in the first of the reactions, the ettringite reacts with the gypsum and water to form ettringite, lime and alumina hydroxides, i.e.
Ferrite + gypsum + water ® ettringite + ferric aluminum hydroxide + lime C 4 AF + 3C S H 2 + 3H ® C 6 (A,F) S 3 H 32 + (A,F)H 3 + CH
the ferrite further reacts with the ettringite formed above to produce garnets, i.e.
Ferrite + ettringite + lime + water ® garnets C 4 AF + C 6 (A,F) S 3 H 32 + 2CH +23H ® 3C 4 (A,F) S H 18 + (A,F)H 3
The garnets only take up space and do not in any way contribute to the strength of the cement paste. The hardened cement paste Hardened paste consists of the following: Ettringite – 15 to 20% Calcium silicate hydrates, CSH – 50 to 60% Calcium hydroxide (lime) – 20 to 25% Voids – 5 to 6% (in the form of capillary voids and entrapped and entrained air) Conclusion It can therefore be seen that each of the compounds in cement has a role to play in the hydration process.
- By changing the proportion of each of the constituent compounds in the cement (and other factors such as grain size), it is possible to make different types of cement to suit several construction needs and environment.
- References: Sidney Mindess & J.
- Francis Young (1981): Concrete, Prentice-Hall, Inc., Englewood Cliffs, NJ, pp.671.
Steve Kosmatka & William Panarese (1988): Design and Control of Concrete Mixes, Portland Cement Association, Skokie, Ill. pp.205. Michael Mamlouk & John Zaniewski (1999): Materials for Civil and Construction Engineers, Addison Wesley Longman, Inc.,
What is responsible for the early strength?
Discussion :: Building Materials – Section 3 ( Q.No.2 ) –
|PRITHVI said: (May 30, 2014)|
|Early gain of strength is caused due to tricalcium silicate and thus setting time too.|
Civil Engineering – Building Materials – Discussion
What are the three components of a strength?
When it comes to strength training for athletes, we can break it up into three components: Stability Training. Strength Training. Power Training.
What affects the strength of cement?
🕑 Reading time: 1 minute Concrete strength is affected by many factors, such as quality of raw materials, water/cement ratio, coarse/fine aggregate ratio, age of concrete, compaction of concrete, temperature, relative humidity and curing of concrete.
What gives concrete its strength?
« Back to Help & Advice Concrete is a fantastic material that is used worldwide to create some of the most impressive, strong and long lasting structures. Suitable for a whole range of constructions, including pavements, houses, skyscrapers, dams and bridges, the strength of concrete very rarely fails to hold up. The most simple answer comes down to the production process: concrete is produced when a paste of portland cement and water is mixed with both small and large aggregates. When the paste and aggregates meet, the paste coats the surface of the aggregate and a chemical reaction called hydration takes places, causing the paste to harden and the entire mixture to gain strength.
- The science The science behind the reaction is a little more complex: Concrete is a composite material that is made up of a binder (the cement paste) and a filler (aggregate), which when mixed form chemical bonds with water molecules to become hydrated.
- This hydration causes the concrete to cure.
- The tricalcium silicate compound is responsible for most of the strength of concrete, releasing calcium ions, hydroxide ions and heat, which speeds up the reaction process.
Once the material is saturated with calcium and hydroxide ions, calcium hydroxide begins to crystallise and calcium silicate hydrate forms. The production of crystallisation leads to more and more calcium silicate hydrate forming and thickening until the water molecules’ path is blocked and there are no longer any empty, weak spaces in the mixture.
- This results in a very low porous, and therefore very strong, structure.
- Even stronger concrete Following the science behind the creation of concrete, there are simple steps that can be taken to make concrete even stronger.
- High-strength concrete is created by simply adjusting the ratios of cement, water, aggregates and admixtures to form stronger bonds that make for more robust, long lasting concrete.
The lower the water to cement ratio, the stronger the mix will be, but as water is an essential element to the hydration process, it is necessary to ensure that enough is still used to saturate the mixture. In general, cement is made with a water to cement mass ratio of between 0.35-0.6. Click image for full size view As well as being immensely strong and popular for use in construction, concrete has a rather interesting history; read our 8 amazing facts about concrete here! Concrete use dates back to Egyptian times Yes, even the early Egyptians saw the benefits of using concrete in their buildings, with a primitive form made from gypsum and lime being used as infill in the construction of the pyramids over 5,000 years ago.
Mud and straw was used to form the bricks. The world’s largest unreinforced concrete dome still stands today Located in Rome, the Pantheon was commissioned by Marcus Agrippa as a temple to all the ancient Roman gods, but sadly both this and the second structure caught on fire. The third Pantheon, which is still standing today, was finished under the rule of the emperor Hadrian in 126AD.
Standing at 43 metres tall and 43 metres wide, this dome is still the world’s largest unreinforced (without steel bearers) dome today, beating out other impressive structures such as St. Peter’s Basilica. Thanks to the durability and longevity of concrete, the Pantheon is considered to be one of the best preserved buildings of ancient Rome You can get bubblegum scented concrete Yes, you read that right! Construction companies such as Quintechs LLC have been experimenting with decorative concrete, including making concrete smell more appealing. Smells available include bubblegum, vanilla, thyme, coffee and lavender.
- On large concrete structures the scented form release agents are applied directly onto cured concrete where they react with the alkali present and bond, emitting a pleasant smell.
- Concrete makes up one of the Seven Wonders of the World The Statue of Christ the Redeemer, located in Brazil, is built from reinforced concrete and soapstone.
The statue took nine years to complete through the 1920s and weighs in at 635 tonne with a height of 30.1 metres. Concrete was used during World War II to detect approaching aircrafts Huge concrete dishes, often referred to as ‘concrete ears’ or ‘sound mirrors’, were erected along the south coast of England during the Second World War.
Small microphones were suspended above the dishes, allowing a listener to detect approaching aircraft up to 27 miles away. The advancements in technology, however, soon made these systems obsolete. The oldest piece of concrete on record is 12 million years old The oldest ever piece of concrete is over 12 million years old and was found in Israel in the 1960s.
The natural deposit was formed when an oil shale had exploded near limestone and when the two touched, a layer of concrete was formed. Thomas Edison saw the potential of concrete Thomas Edison had 49 patents experimenting with single pour concrete houses and furniture, including refrigerators and pianos, which he thought could be built in a single pour with the right mold. Unfortunately, production scale was limited and the production wasn’t financially viable, otherwise who’d have known what we’d be using concrete for now! Man-made cement was invented by a Leeds Bricklayer In 1824, an English bricklayer named Joseph Aspdin patented portland cement after many previous failed attempts.
Aspdin began by mixing clay and limestone together, and when this mixture burned a fine powder was created, which he named after Portland because it reminded him of a stone on the isle. This creation radicalised the construction industry as it was so fast-setting and aesthetically attractive. If you’re looking for high quality concrete suppliers in Essex, look no further than Neil Sullivan and Sons.
We are well experienced in all aspects of concrete services for both domestic and commercial projects, including supplying volumetric concrete and on-site mixed concrete, floor screed and aggregates, For more information, get in contact today.
How does cement gain strength?
Many factors influence the rate at which the strength of concrete increases after mixing. Some of these are discussed below. First, though a couple of definitions may be useful: The processes of ‘setting’ and ‘hardening’ are often confused: Setting is the stiffening of the concrete after it has been placed.
- A concrete can be ‘set’ in that it is no longer fluid, but it may still be very weak; you may not be able to walk on it, for example.
- Setting is due to the formation of ettringite and early-stage calcium silicate hydrate.
- The terms ‘initial set’ and ‘final set’ are commonly used; these are arbitrary definitions of early and later set.
There are laboratory procedures for determining these using weighted needles penetrating into cement paste. Hardening is the process of strength growth and may continue for weeks or months after the concrete has been mixed and placed. Hardening is due largely to the formation of calcium silicate hydrate as the cement continues to hydrate.
How can we increase the strength of cement?
Increasing Concrete Strength Compressive strength is the most common performance metric for concrete, The compressive strength of concrete can be increased by:
Including admixturesAdjusting the cement type and quantityReducing the water/cement ratioUtilizing supplementary cementitious materials (SCMs)Altering the aggregates – type and gradations
Additionally, high-early strength concrete can be achieved through a, : Increasing Concrete Strength