Water-Cement Ratio and It’s Importance Water-Cement ratio means the ration between weight of water to the weight of cement used while preparing concrete mix. Water Cement ratio plays important role in developing the strength of concrete. The water-cement ratio is also responsible for the porosity of the hardened cement paste. Water-cement theory states that for a given combination of materials and as long as workable consistency is obtained, the strength of concrete at a given age depends on w/c ratio. In 1918, Duff Abrams made water cement ratio law for strength of concrete. σc = compressive strength at some fixed age A = empirical constant (96.5 MPa) B = constant that depends mostly on the cement properties (about 4) & water cement ratio by weight.
- 1 What is the ideal water-cement ratio for hand?
- 2 What is water Cement law?
- 3 What is the water-cement ratio for M25 grade concrete?
- 4 How do you mix water-cement ratio?
What is the minimum water-cement ratio for concrete?
The water–cement ratio ( w/c ratio, or water-to-cement ratio, sometimes also called the water-cement factor, f ) is the ratio of the mass of water ( w ) to the mass of cement ( c ) used in a concrete mix: The typical values of this ratio f = w ⁄ c are generally comprised in the interval 0.40 and 0.60. The water-cement ratio of the fresh concrete mix is one of the main, if not the most important, factors determining the quality and properties of hardened concrete, as it directly affects the concrete porosity, and a good concrete is always a concrete as compact and as dense as possible.
- A good concrete must be therefore prepared with as little water as possible, but with enough water to hydrate the cement minerals and to properly handle it.
- A lower ratio leads to higher strength and durability, but may make the mix more difficult to work with and form.
- Workability can be resolved with the use of plasticizers or super-plasticizers,
A higher ratio gives a too fluid concrete mix resulting in a too porous hardened concrete of poor quality. Often, the concept also refers to the ratio of water to cementitious materials, w/cm. Cementitious materials include cement and supplementary cementitious materials such as ground granulated blast-furnace slag (GGBFS), fly ash (FA), silica fume (SF), rice husk ash (RHA), metakaolin (MK), and natural pozzolans,
Most of supplementary cementitious materials (SCM) are byproducts of other industries presenting interesting hydraulic binding properties. After reaction with alkalis (GGBFS activation) and portlandite ( Ca(OH) 2 ), they also form calcium silicate hydrates (C-S-H), the “gluing phase” present in the hardened cement paste.
These additional C-S-H are filling the concrete porosity and thus contribute to strengthen concrete. SCMs also help reducing the clinker content in concrete and therefore saving energy and minimizing costs, while recycling industrial wastes otherwise aimed to landfill,
- The effect of the water-to-cement (w/c) ratio onto the mechanical strength of concrete was first studied by René Féret (1892) in France, and then by Duff A.
- Abrams (1918) (inventor of the concrete slump test ) in the USA, and by Jean Bolomey (1929) in Switzerland.
- The 1997 Uniform Building Code specifies a maximum of 0.5 w/c ratio when concrete is exposed to freezing and thawing in moist conditions or to de-icing salts, and a maximum of 0.45 w/c ratio for concrete in severe, or very severe, sulfate conditions.
Concrete hardens as a result of the chemical reaction between cement and water (known as hydration and producing heat ). For every mass ( kilogram, pound, or any unit of weight ) of cement (c), about 0.35 mass of water (w) is needed to fully complete the hydration reactions.
However, a fresh concrete with a w/c ratio of 0.35 may not mix thoroughly, and may not flow well enough to be correctly placed and to fill all the voids in the forms, especially in the case of a dense steel reinforcement, More water is therefore used than is chemically and physically necessary to react with cement.
Water–cement ratios in the range of 0.40 to 0.60 are typically used. For higher-strength concrete, lower w/c ratios are necessary, along with a plasticizer to increase flowability. A w/c ratio higher than 0.60 is not acceptable as fresh concrete becomes “soup” and leads to a higher porosity and to very poor quality hardened concrete as publicly stated by Prof.
Gustave Magnel (1889-1955, Ghent University, Belgium) during an official address to American building contractors at the occasion of one of his visits in the United States in the 1950’s to build the first prestressed concrete girder bridge in the USA: the Walnut Lane Memorial Bridge in Philadelphia open to traffic in 1951.
The famous sentence of Gustave Magnel, facing reluctance from a contractor, when he was requiring a very low w/c ratio, zero-slump, concrete for casting the girders of this bridge remains in many memories: “American makes soup, not concrete”, When the excess water added to improve the workability of fresh concrete, and not consumed by the hydration reactions, leaves concrete as it hardens and dries, it results in an increased concrete porosity only filled by air,
A higher porosity reduces the final strength of concrete because the air present in the pores is compressible and concrete microstructure can be more easily ” crushed “. Moreover, a higher porosity also increases the hydraulic conductivity ( K, m/s) of concrete and the effective diffusion coefficients ( D e, m 2 /s) of solutes and dissolved gases in the concrete matrix.
This increases water ingress into concrete, accelerates its dissolution ( calcium leaching ), favors harmful expansive chemical reactions ( ASR, DEF), and facilitates the transport of aggressive chemical species such as chlorides ( pitting corrosion of reinforced bars ) and sulfates (internal and external sulfate attacks, ISA and ESA, of concrete) inside the concrete porosity.
- When cementitious materials are used to encapsulate toxic heavy metals or radionuclides, a lower w/c ratio is required to decrease the matrix porosity and the effective diffusion coefficients of the immobilized elements in the cementitious matrix.
- A lower w/c ratio also contributes to minimize the leaching of the toxic elements out of the immobilization material.
A higher porosity also facilitates the diffusion of gases into the concrete microstructure, A faster diffusion of atmospheric CO 2 increases the concrete carbonation rate, When the carbonation front reaches the steel reinforcements (rebar), the pH of the concrete pore water at the steel surface decreases.
At a pH value lower than 10.5, the carbon steel is no longuer passivated by an alkaline pH and starts to corrode ( general corrosion ). A faster diffusion of oxygen ( O 2 ) into the concrete microstructure also accelerates the rebar corrosion. Moreover, on the long term, a concrete mix with too much water will experience more creep and drying shrinkage as excess water leaves the concrete porosity, resulting in internal cracks and visible fractures (particularly around inside corners), which again will reduce the concrete mechanical strength.
Finally, water added in excess also facilitates the segregation of fine and coarse aggregates ( sand and gravels ) from the fresh cement paste and causes the formation of honeycombs (pockets of gravels without hardened cement paste) in concrete walls and around rebar.
It also causes water bleeding at the surface of concrete slabs or rafts (with a dusty surface left after water evaporation). For all the afore mentioned reasons, it is strictly forbidden to add extra water to a ready-mix concrete truck when the delivery time is exceeded, and the concrete becomes difficult to pour because it starts to set.
Such diluted concrete immediately loses any official certification and the responsibility of the contractor accepting such a deleterious practice is also engaged. In the worst case, an addition of superplasticizer can be made to increase again the concrete workability and to salvage the content of a ready-mix concrete truck when the maximum concrete delivery time is not exceeded.
What is the ideal water-cement ratio for hand?
Basic Civil Engineering Questions and Answers – Composition of Concrete This set of Basic Civil Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Composition of Concrete”.1. How many components are mainly used to prepare concrete? a) 5 b) 3 c) 2 d) 4 View Answer Answer: d Explanation: Concrete is prepared by mixing cement, fine aggregate, coarse aggregate with water.
- It is a thick paste and hence has high bulk density.2.
- Which of the below is the most common alternative to cement in concrete? a) Slag b) Fly ash c) Asphalt d) Lime View Answer Answer: c Explanation: Asphalt is the highly cementitious material.
- It possesses almost all qualities of cement and is widely used as an alternative to cement.3.
What is the ideal water-cement ratio to be used while hand mixing? a) 0.4-0.5 b) 0.5-0.6 c) 0.6-1 d) 1.6-2 View Answer Answer: b Explanation: Ideal water cement ratio for general works is 0.45. During machine mixing, it can be in the range of 0.4-0.5.
Hand mixing is done by labourers and maximum 0.6 can be allowed.4. Which IS code gives details regarding water to be used in concrete? a) IS 456 b) IS 383 c) IS 565 d) IS 3012 View Answer Answer: a Explanation: Normally, potable water is to be used for preparing concrete. In the case where potable water is not available, a certain amount of impurities are permissible in the water to be used.
Those are given in Table in IS 456.5. How many types of chemical admixture are there? a) 2 b) 3 c) 4 d) 5 View Answer Answer: c Explanation: Admixtures are compounds added to concrete to attain specific properties. The chemical admixtures are added in small amounts.
The 4 types are accelerators, retarders, plasticizers and air entraining agents.6. Retarders are used for: a) Construction of high rise building b) Repair works c) Cold weather conditions d) Grouting deep oil wells View Answer Answer: d Explanation: Retarders are used to slow down the initial rate of hydration and extend the initial setting time.
It is therefore used to grout deep oil wells, transport RMC (Ready Made Concrete) and avoid cold joints. Accelerator is used for first 3 options.7. _ is added to make white concrete. a) Fly ash b) Metakaolin c) Rise husk d) Pigments View Answer Answer: b Explanation: Fly ash, Rise husk are dark in colour.
Metakaolin is usually bright white in colour and is the preferred choice for architectural concrete where appearance is important.8. As water cement ratio increases, _ also increases. a) Compressive strength b) Tensile strength c) Bleeding d) Workability View Answer Answer: d Explanation: More water improves the workability of a mix, but compromises on the strength requirements.
Hence, ideal w/c ratio of 0.45 is to be used.9. Which of the below is an example of plasticizer? a) Hydroxylated carboxylic acid b) Fluoro-silicate c) Gypsum d) Surkhi View Answer Answer: a Explanation: Fluoro-silicate is an accelerator. Gypsum is a retarder and surkhi is a type of mineral admixture.10.
Which component of concrete gives it desired compressive strength? a) Water b) Cement c) Aggregates d) Admixture View Answer Answer: c Explanation: Aggregates used are sand, gravel or crushed stones. These have high compressive strength. Concrete is strong in compression and weak in tension due to this reason.11.
What is the ratio of the component in grade M20 concrete? a) 1:3:6 b) 1:1.5:3 c) 1:1:2 d) 1:2:4 View Answer Answer: b Explanation: Concrete is graded into many types as per IS 456-2000. M stands for mix and the number, say, 20 is a compressive strength after 28 days in N/mm 2,
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Is 456 minimum water-cement ratio?
According to IS 456-2000, the minimum grade of concrete with maximum free water to cement ratio of 0.5 and minimum cement content of 300 kg/m 3 is.
Does 456-2000 recommend to provide a minimum?
Yes, D is the answer. IS 456-2000 Recommends providing certain minimum steel in a RCC beam. Answer : to provide enough ductility to the beam. Sometimes minimum steels are provided beam first ductility and second time of rupture and flexure failure.
What is water Cement law?
Water Cement Ratio and Abrams’ law Duff Abrams published data that showed that for a given set of concreting materials, the strength of the concrete depends solely on the relative quantity of water compared with the cement. In other words, the strength is a function of the water to cement ratio (w/c) where w represents the mass of water and c represents the mass of cement.
- This became known as Abrams law and it remains valid today as it was in 1918.
- However, more often, w/cm is used and cm represents the mass of cementing materials, which includes the portland cement plus any supplementary cementing materials such as fly ash, slag cement, or silica fume.
- Unnecessarily high water content dilutes the cement paste (the glue of concrete) and increases the volume of the concrete produced.
Some advantages of reducing water content include:
Increased compressive and flexural strength Lower permeability and increased watertightness Increased durability and resistance to weathering Better bond between concrete and reinforcement Reduced drying shrinkage and cracking Less volume change from wetting and drying
The less water used, the better the quality of the concrete provided themixture can still be consolidated properly.Smaller amounts of mixing water result in stiffer mixtures; with vibration, stiffer mixtures can be easily placed. Thus, consolidation by vibration permits improvement in the quality of concrete.
Reducing the water content of concrete, and thereby reducing the w/cm, leads to increased strength and stiffness, and reduced creep. The drying shrinkage and associated risk of cracking will also be reduced. The concrete will have a lower permeability or increased water tightness that will render it more resistant to weathering and the action of aggressive chemicals.
The lower water to cementitious materials ratio also improves the bond between the concrete and embedded steel reinforcement. esolution Construction&Engineering : Water Cement Ratio and Abrams’ law
What is the water-cement ratio for M25 grade concrete?
How much water required for M20 concrete? – For M20 concrete they are mixed in the ratio of 1:1.5:3 (1 part cement to 1.5 parts sand & 3 parts aggregate by volume) to gain 20 MPa strength of concrete and water should be added in the range of 55% of weight of cement in moderate exposure condition for M20 concrete.
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- Calculate how much water do you need for 1m3 of m20 concrete in following steps:-
● dry volume of concrete = 1× 1.54 = 1.54m3 ● calculate part of cement in mix, total proprtion such as 1 + 1.5+3 = 5.5, then quantity of cement = 1/5.5 of dry volume ● calculate required cement quantity = 1/5.5 × 1.54 × 1440 kg/m3 = 403kg ● calculate required quantity of water, as 0.55 is w/c ratio for m20 concrete, so quantity of water = 403 × 0.55 = 220 litres.
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: How much water do i need for 1m3 of M15, M20 & M25 concrete
What is ratio of cement water and sand?
A general teacher’s guide for concrete preparation – The physical properties of density and strength of concrete are determined, in part, by the proportions of the three key ingredients, water, cement, and aggregate. You have your choice of proportioning ingredients by volume or by weight.
Proportioning by volume is less accurate, however due to the time constraints of a class time period this may be the preferred method. A basic mixture of mortar can be made using the volume proportions of 1 water : 2 cement : 3 sand. Most of the student activities can be conducted using this basic mixture.
Another “old rule of thumb” for mixing concrete is 1 cement : 2 sand : 3 gravel by volume. Mix the dry ingredients and slowly add water until the concrete is workable. This mixture may need to be modified depending on the aggregate used to provide a concrete of the right workability.
- The mix should not be too stiff or too sloppy.
- It is difficult to form good test specimens if it is too stiff.
- If it is too sloppy, water may separate (bleed) from the mixture.
- Remember that water is the key ingredient.
- Too much water results in weak concrete.
- Too little water results in a concrete that is unworkable.
- If predetermined quantities are used, the method used to make concrete is to dry blend solids and then slowly add water (with admixtures, if used).
- It is usual to dissolve admixtures in the mix water before adding it to the concrete. Superplasticizer is an exception.
- Forms can be made from many materials. Cylindrical forms can be plastic or paper tubes, pipe insulation, cups, etc. The concrete needs to be easily removed from the forms. Pipe insulation from a hardware store was used for lab trials. This foam-like material was easy to work with and is reusable with the addition of tape. The bottom of the forms can be taped, corked, set on glass plates, etc. Small plastic weighing trays or Dairy Queen banana split dishes can be used as forms for boats or canoes.
- If compression tests are done, it may be of interest to spread universal indicator over the broken face and note any color changes from inside to outside. You may see a yellowish surface due to carbonation from CO 2 in the atmosphere. The inside may be blue due to calcium hydroxide.
- To answer the proverbial question, “Is this right?” a slump test may be performed. A slump test involves filling an inverted, bottomless cone with the concrete mixture. A Styrofoam or paper cup with the bottom removed makes a good bottomless cone. Make sure to pack the concrete several times while filling the cone. Carefully remove the cone by lifting it straight upward. Place the cone beside the pile of concrete. The pile should be about 1/2 to 3/4 the height of the cone for a concrete mixture with good workability. (SEE DIAGRAM)
- To strengthen samples and to promote hydration, soak concrete in water (after it is set).
- Wet sand may carry considerable water, so the amount of mix water should be reduced to compensate.
- Air bubbles in the molds will become weak points during strength tests. They can be eliminated by:
- i. packing the concrete.
- ii. Tapping the sides of the mold while filling the mold.
- iii. “rodding” the concrete inside the mold with a thin spatula.
- Special chemicals called “water reducing agents” are used to improve workability at low water to cement ratios and thus produce higher strengths. Most ready-mix companies use these chemicals, which are known commercially as superplasticizers. They will probably be willing to give you some at no charge.
- You can buy a bag of cement from your local hardware store. A bag contains 94 lb. (40kg) of cement. Once the bag has been opened, place it inside a garbage bag (or two) that is well sealed from air. This will keep the cement fresh during the semester. An open bag will pick up moisture and the resulting concrete may be weaker. Once cement develops lumps, it must be discarded. The ready mix company in your area may give you cement free of charge in a plastic pail.
What is a typical water-cement ratio for normal strength concrete?
Why the Water-Cement Ratio In Concrete Materials Ratio Matters – The water-cement ratio is the weight of the water in your concrete relative to the weight of cement. Normally, according to IS code 10262 (2009), your nominal mix should have a ratio between 0.4 and 0.6.
However, depending on the type of concrete, the compressive strength you need and your environment, you may want a higher or lower ratio. If you add more water, you may have an easier time working with your cement. The problem is that if you add too much water, once the aggregates settle, the water will evaporate, which leaves voids in the concrete.
The more and bigger voids you have, the weaker your concrete is. You need to add the right amount of water for cement workability without leaving you in a situation where your concrete is too weak when it hardens.
What is 0.5 in water-cement ratio?
Calculation of Water Quantity for Concrete – As you can see from the Chart, the W/C Ratio varies from 0.4 to 0.7 depending on exposure conditions.
- If we need to calculate Water quantity for concrete, first find the cement content for the volume.
- If we Assume the required cement volume as 50kg,
- Required amount of water = W/C Ratio X Cement Volume
Therefore, Required amount of water = 0.5 X 50 kg = 25 litres / 50 kg cement bag. For Design mix, the W/C Ratio will depend upon the workability, strength requirements. In ANNEX A. they have explained the process for design mix. Hope that helps you.
How do you mix water-cement ratio?
HOW TO CALCULATE WATER CEMENT RATIO – The water to cement ratio is calculated by dividing the water in one cubic yard of the mix ( in pounds) by the cement in the mix (in pounds). So if one cubic yard of the mix has 235 pounds of water and 470 pounds of cement- the mix is a,50 water to cement ratio.