# Dip the cloth in cement mixture – Take a piece of cloth like old towel, fleece blanket or a rug that you want to turn into a sturdy planter. Dip it in the cement mixture so that it completely gets coated with a layer of the mixture. Once it is fully saturated, you can place it on the desired mold to give it a specific shape. Use a bucket to give it the desired shape and pattern.
- 1 How do you make lightweight concrete pots?
- 2 Does a concrete planter need to be sealed?
- 3 Why are my cement pots cracking?
- 4 What is the best mix for concrete?
What do you mix with cement to make pots?
Mixing Cement For A Planter – A typical cement pots recipe is two cups of concrete or cement and about half a cup of water. This is the proper ratio for many mixes- if you are making a small planter. Some mixes require the addition of sand, but most do not. This consistency is helpful so that you can pour it in and so that it will get into the grooves. For other types of planters, you will want an apple sauce-like consistency.
How do you make lightweight concrete pots?
What you do: –
- 1. Once you have your materials together, it’s time to mix. Wear rubber gloves, a dust mask to avoid breathing cement dust, and safety goggles to protect eyes from dust. Mix 3 parts perlite, 3 parts coir, and 2 parts cement in a plastic tub. (Or 1.5:1.5:1 parts). How much you need depends on how large your pot will be. (You can have a small pot project on the side to use up the excess mix.)
- 2. Add water to tub, a bit at a time, until the mixture has the consistency of moist cottage cheese. If you add too much water, then you risk it being too wet. You should be able to squeeze a handful and it holds its shape, and only a few drops of water are released. If you squeeze the mixture and it feels squishy, and you can see water, then it’s too wet.
- 3. Spray inside of your chosen mould with cooking oil. Sophie also uses a short length of hose, sprayed with oil, to create a drainage hole; cork or dowel would also work.
- 4. Holding the drainage hole plug in place, push a handful of wet hypertufa mixture firmly against the bottom of the mould. Repeat until you have made a bottom base that is approximately 2.5cm thick. Push handfuls of wet hypertufa mixture firmly against the sides of container approximately 2cm thick. Continue until rim of mould is reached. Press bottom and sides firmly to remove air pockets. An alternative is to use a small object inside the mould to shape it; Sophie fills a large bucket and places a smaller bucket inside to create a more even finish.
- 5. Cover with plastic and let dry for between 24 – 48 hours.
- 6. Take off the plastic bag and remove the pot, which will be slightly wet, from mould. Using a wire brush or sandpaper sponge, rough up the surface of the hypertufa for a more rustic appearance. If your pot falls apart when you take it out of the mould, it may have been removed too early, or the mix was too wet.
- 7. Let your new pot “cure” by sitting it out of the weather for 2 to 3 weeks to dry completely.
- 8. Once your new pot is cured, it’s ready for use. It can be placed outside and used like any other pot.
There are many options to explore with the wonderful world of Hypertufa. Other options include using dyes or pebbles in the mix, or wrapping the outside of the pot with a mesh fabric or dried leaves to create an interesting pattern. Filmed on Peramangk country Broadcast 28 Aug 2020 28 Aug 2020 Fri 28 Aug 2020 at 9:30am : Hip Hip Hypertufa – DIY Lightweight Cement Pots – Gardening Australia
Does a concrete planter need to be sealed?
Do concrete planters need to be sealed? Concrete pots only need to be sealed if you are growing a plant in the pot that needs more acidic soil. You see, concrete contains lime which can cause the soil to become alkaline. This is a good environment for succulents, but many plants will not be happy in this soil.
What are the three 3 ingredients that make up premixed concrete?
Contrary to popular belief, concrete and cement are not the same thing; cement is actually just a component of concrete. Concrete is made up of three basic components: water, aggregate (rock, sand, or gravel) and Portland cement. Cement, usually in powder form, acts as a binding agent when mixed with water and aggregates.
- This combination, or concrete mix, will be poured and harden into the durable material with which we are all familiar.
- Find concrete contractors near me,
- Following is a group of articles that will be helpful when trying to understand more about concrete and cement.
- Other items that might be of interest to you include concrete basics such as mix design, and cement information,
Popular Concrete Topics: What is Concrete? Time: 00:52 What is concrete made of? Portland cement, aggregate, sand, etc. Find Concrete Ready Mix Suppliers Article Contents: Components of a Basic Concrete Mix Desired Properties of Concrete Concrete Admixtures Concrete Reinforcement: Fibers vs.
Portland Cement Water Aggregates (rock and sand)
Portland Cement – The cement and water form a paste that coats the aggregate and sand in the mix. The paste hardens and binds the aggregates and sand together. Water – Water is needed to chemically react with the cement (hydration) and too provide workability with the concrete.
The amount of water in the mix in pounds compared with the amount of cement is called the water/cement ratio. The lower the w/c ratio, the stronger the concrete. (higher strength, less permeability) Aggregates – Sand is the fine aggregate. Gravel or crushed stone is the coarse aggregate in most mixes. Podcast: Hear Jim Peterson, founder of ConcreteNetwork.com, answer top concrete questions on the Ask Danny podcast from Today’s Homeowner,
Desired Properties of Concrete 1. The concrete mix is workable, It can be placed and consolidated properly by yourself or your workmen.2. Desired qualities of the hardened concrete are met: for example, resistance to freezing and thawing and deicing chemicals, watertightness (low permeability), wear resistance, and strength.
use the stiffest mix possible use the largest size aggregate practical for the job. Use the optimum ratio of fine to coarse aggregate.
Discuss how to achieve your goals for the concrete with your ready mix supplier. Concrete Admixtures: Most Common Types and What They Do Admixtures are additions to the mix used to achieve certain goals. Here are the main admixtures and what they aim to achieve.
Accelerating admixture- accelerators are added to concrete to reduce setting time of the concrete and to accelerate early strength. The amount of reduction in setting time varies depending on the amount of accelerator used (see your ready mix supplier and describe your application). Calcium chloride is a low cost accelerator, but specifications often call for a nonchloride accelerator to prevent corrosion of reinforcing steel.
Retarding admixtures -Are often used in hot weather conditions to delay setting time. They are also used to delay set of more difficult jobs or for special finishing operations like exposing aggregate. Many retarders also act as a water reducer. Fly Ash – Is a by product of coal burning plants.
Fly ash improves workability Fly ash is easier to finish Fly ash reduces the heat generated by the concrete Fly ash costs to the amount of the cement it replaces
Air Entraining Admixtures – must be used whenever concrete is exposed to freezing and thawing, and to deicing salts. Air entraining agents entrains microscopic air bubbles in the concrete: when the hardened concrete freezes, the frozen water inside the concrete expands into these air bubbles instead of damaging the concrete.
Air entrainment improves concrete workability Air entrainment improves durability Air entrainment produces a more workable mix
Water reducing admixtures -reduces the amount of water needed in the concrete mix. The water cement ratio will be lower and the strength will be greater. Most low range water reducers reduce the water needed in the mix by 5%-10%. High range water reducers reduce the mix water needed by 12% to 30% but are very expensive and rarely used in residential work.
Concrete Reinforcement: Fibers vs. Welded Wire Mesh Fibers can be added to the concrete mix in lieu of welded wire mesh. The problem with welded wire mesh is that it often ends up on the ground from being stepped on as the concrete is being placed. (particularly if no support blocks are used). Another problem is that mesh does not prevent or minimize cracking-it simply holds cracks that have already occurred together.
If you could look into a section of concrete poured with fibers you would see millions of fibers distributed in all directions throughout the concrete mix. As micro cracks begin to appear due to shrinkage as water evaporates form the concrete (plastic shrinkage), the cracks intersect with the fibers which block their growth and provide higher tensile strength capacity at this crucial time.
Click here for how fibers are an important part of ” how to build high quality slabs on grade.” ADJUSTING CONCRETE MIXES TO CORRECT PLACING PROBLEMS When the concrete sticks to the trowel when it is lifted off the concrete, or concrete sticks to the finishers kneeboards, too much sand in the mix or higher than necessary air entrainment are most likely the causes.
Excessive bleedwater will delay the finishing operation and can cause serious problems with the surface of the concrete. Adding more sand to the mix, adding more entrained air, using less mix water, or adding cement or fly ash are possible cures. Make sure your ready mix supplier knows if you will be pumping concrete.
Pumping mixes require a sufficient amount of fines and there are limits to the size of the aggregate in order for the mix to be pumpable. Fly ash and air entrainment improve workability and pumpability. Setting time of the mix can be slowed with retarders. The mix may be cooled in hot weather by replacing part of the mixing water with ice, sprinkling water on the aggregate pile at the ready mix plant, or injecting liquid nitrogen into the batch.
Setting time of the mix can be sped up with accelerators. The mix can be heated at the ready mix plant by heating the mix water and aggregates. Installing Concrete Placing Concrete Normal concrete weighs approximately 150 pounds per cubic foot and should be placed as near as possible to its final position.
- Excess handling can cause segregation of the course and fine aggregates.
- Wetting up the concrete so it can be raked or pushed into a location far from where it is discharged is not acceptable.
- Concrete is poured directly from the chute of the ready mix truck, wheeled into place with a buggy, or pumped into place with a concrete boom pump (see concrete pumping ).
Concrete is normally specified at a 4-5″ slump. Industrial, commercial, and some residential projects require an inspector on concrete pours who monitors the concrete slump and takes slump measurements at the required intervals. Also see, How To Build High Quality Slabs on Grade Spreading Concrete The purpose of spreading fresh concrete is to place concrete as close as possible to finish level to facilitate straightedging/screeding the concrete.
Short handled, square ended shovels are recommended for spreading concrete. A come-along (a tool that looks like a hoe and has a long straight edged blade) can also be used. Do not use a round edge shovel for spreading concrete since it does not spread the concrete evenly. Any spreader used should be rigid enough to push and pull wet concrete without bending: Normal concrete weighs approximately 150 pounds per cubic foot.
Cold weather concreting Hot weather concreting Curing concrete Decorative Concrete Introduction to decorative concrete Decorative concrete glossary Concrete countertop glossary Concrete History : An Interactive Timeline Concrete Contractors: Find A Concrete Product Supplier or Distributor Other Concrete Resources What is Concrete?- University of Illinois Urbana-Champaign Concrete Industry Management- Middle Tennessee State University ACI Free Downloads- American Concrete Institute (ACI) Cement and Concrete Basics- Portland Cement Association (PCA)
Why are my cement pots cracking?
Reason 2. Climate Conditions During Curing Causes Cracking In Concrete Pots – You can end up with cracking if the weather conditions are windy or very dry when your concrete pot is curing. This is essentially the same problem as too much water in the mix. The wind and lack of humidity are causing the concrete to shrink quickly, forcing it to crack.
- The easiest solution for preventing the concrete from losing too much water is to wrap it in plastic while it’s curing.
- You can even mist it with water first and then wrap it if you want to play it a bit safer.
- Using plastic to keep in moisture is what is referred to as wet curing,
- Please see my *Note below about my projects and wet curing.
- By the way, if you are looking for some ideas for I found 17 cold hardy plants that are great for this.
What is the mix for lightweight concrete?
W hat Is Lightweight Concrete? – Lightweight concrete is a mixture made with lightweight coarse aggregates such as shale, clay, or slate, which give it its characteristic low density. Structural lightweight concrete has an in-place density of 90 to 115 lb/ft³, whereas the density of regular weight concrete ranges from 140 to 150 lb/ft³.
- This makes lightweight concrete ideal for building modern structures that require minimal cross sections in the foundation.
- It is being increasingly used to build sleek foundations, and has emerged as a viable alternative to regular concrete.
- Nevertheless, a higher compressive strength of 7000 to 10,000 psi can be attained with lightweight concrete.
However, this may compromise the density of the mixture as it requires the addition of more pozzolans and water-reducing admixtures to the concrete.
How thick should a cement planter be?
The standard wall thickness cast for Form and Fiber’s box concrete planters is as follows: – 3.0′ Minimum wall thickness for planters up to 6′-0′ L – 3.5′ thickness for planters over 6′-0′ L (72′) – 4.0′ thickness for planters over 8′-0′ L (96′), with manufacturer approval for overall size of box.
Do you paint inside concrete planters?
How to Paint and Replant Concrete Planters Save yourself the hassle of having to remove paint drips and splatters from your front porch by first maneuvering the planter onto a disposable surface, like a bit of leftover shipping cardboard. Tip : Enlist the help of a friend if the planter is too heavy to move alone.
Typically, you can lift the entire contents of a concrete container out in one piece, as we have here — especially if the soil is dry. Set the old plants aside and be sure to relocate any perennials you want to plant in other locations. Using the sharp edge of the metal scraper, remove as much loose, flaking paint as you can from all areas, including the top and/or inner edge of the planter (Image 1).
Using the wire brush, remove any remaining stuck-on bits of old paint and go over all areas to smooth the surface (Image 2). First, use a broom and dustpan to sweep up the workspace. Give your planter a good, solid coat of paint on all exterior sides (Image 1).
Also, add an inner ring of paint to the planter’s interior (Image 2). If necessary, allow the first coat to dry, then brush on a second coat. Note : Look at your planter from all angles, including down low to ensure you’ve evenly covered all areas. A solid coat of exterior paint not only looks great but will seal and protect the porous concrete from the elements for many years to come.
After the paint has fully dried, add potting soil, leaving just enough room to add the new plants. You’ve probably heard it before but the successful formula for a container is thriller, filler and spiller. So, you’ll need a central knockout plant/plants for the thriller (we used a single purple salvia surrounded by a pair of Persian shield plants), filler plants that grow in to give the planter a lush look (we used pale purple lantana) and a spiller, or a trailing plant that will spill over the container’s edge (we used lobelia).
To determine placement, set the nursery pots on top of the freshly added layer of potting soil and arrange till you’re happy with their position, being sure to leave each plant a bit of elbow room to accomodate future growth. Remove each plant from its nursery pot by firmly grasping the bottom of the plastic pot while gently pulling the plant free (Image 1).
To give your plant a fresh start in its new home, gently tease apart the roots with your fingers (Image 2) to encourage new growth. Place each unpotted plant in its new location (Image 3) and fill in any gaps with potting soil, gently but firmly pressing the soil around each of the plants to secure them in their new home.
- Finally, no planter is complete without a layer of mulch that not only serves as a decorative finishing touch but also preserves moisture (meaning you’ll need to water less often) and discourages weeds.
- Voila, your decades-old planters have a new lease on life and will look great for many seasons to come.
Sarah Busby; Styling by H. Camille Smith Give your curb appeal a major boost by adding a colorful outdoor rug, cozying up a bench with pillows and popping in more plants in complementary colors (Images 1-3). : How to Paint and Replant Concrete Planters
What happens if you do not seal concrete?
What You Need to Know About Concrete – Concrete is a mixture of water, cement, and either gravel or sand. It has to be mixed carefully using the right amount of each material. Mixing processes help ensure the concrete can be poured and smoothed easily.
- The mixing process also helps with the curing process, which is where the concrete gradually hardens so it is solid and strong.
- Unsealed concrete is porous and can absorb various types of liquids such as water and oil.
- Depending on the type of liquid, it can cause the concrete to become discolored and stained.
The fluids will also cause unsealed concrete to gradually start to deteriorate and break down. This can lead to chipping and concrete driveway cracks.
How do I waterproof my concrete planter?
Correct waterproofing of concrete planters is important to ensure that they remain aesthetically pleasing. Without proper waterproofing, water can migrate to the outside surface of the planter, causing decorative spoiling. Concrete planters can easily be waterproofed using Drybase Elasticised Tanking Slurry,
What is the best mix for concrete?
Four-two-one and the Seven Part Mix Ratio – The safest bet for any concrete mix is four-two-one: four parts crushed rock; two parts sand; and one part cement. The four-two-one mix, obviously, has seven parts. Conveniently, when mixing concrete, the ratio can be mixed on any range of scales.
- That can mean four shovel fulls of rock with two of sand and one of cement; four 5-gallon buckets full of rock, two of sand and one of cement; or four front-end loader buckets full of rock, two sand and one cement.
- But, the four-two-one mixture is not ideal for every situation.
- For those projects that require even extreme compressive strength — the floor of a diesel engine mechanic shop, for example, — a greater amount of rock is required: maybe a five-two-one-and-a-half mix.
For projects that will not require concrete with high compressive strength, but a great degree of workability — a garden fountain, for example, — more sand and less rock is best: a two-four-one mix possibly.
What ingredient makes cement harden?
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.
How do you make homemade cement?
Download Article Download Article The words cement and concrete are used interchangeably, but that’s not technically correct. Cement, in fact, is one of several ingredients that are combined to make concrete. Cement is a powdery, dry substance that makes concrete when it’s mixed with water, gravel, and sand.
- 1 Purchase or collect limestone. If you live near a riverbed or other area where limestone is prevalent, you may be able to find limestone naturally. If not, you’ll need to purchase limestone. It can typically be found at landscaping supply stores, and may be available at large plant nurseries or garden centers.
- If you’re unsure whether or not the rock that you’ve collected is limestone, use a coin to scratch the surface of the rock. Limestone is soft and can be scored by the edge of a coin.
- 2 Break the limestone into small pieces. Take sturdy shovel and stab it into the limestone in order to fracture the rock and break it apart. You’ll be heating the rock in a kiln for an extended period of time, and the smaller you can break up the chunks of rock, the less time you’ll have to heat them.
- Aim to break the limestone into pieces not larger than 2 inches (5.1 cm) across.
- 3 Cook the limestone in a kiln or outdoor oven. In order to ready the limestone for use in cement, place it in a kiln or outdoor wood oven. Turn the kiln up to 900 °C (1,650 °F), and leave the limestone to “bake” for 4 or 5 hours.
- Always wear thick work gloves when working with a kiln. The gloves will also be useful when you’re pulling the baked lime back out of the kiln, since it could severely burn your skin.
- 4 Let the baked limestone cool. After the 4 or 5 hours have passed, pull the baked limestone out of the oven or kiln. Set it nearby and let the chunks cool off before you touch them. Be careful not to breathe in fumes from the baked limestone, as they are caustic and could damage your lungs.
- The baked limestone is called quicklime.
- Consider wearing some kind of respirator when pulling the quicklime out of the kiln. Quicklime is harmful to the body, and even breathing in its dust can harm your lungs.
- 5 Crumble the baked limestone chunks. If the limestone has been baked for long enough, it should have a dry, crumbly consistency. Put on a pair of work gloves and use your hands to crumble the cooled limestone into a fine powder. The resulting powder is cement, which you can mix with water, sand, and gravel to make concrete.
- If you need to store some of the crumbled quicklime for later use, store it in an airtight container.
- 1 Select the right type of cement. Large hardware stores and home-supply stores (such as Lowe’s or Home Depot) will stock a large variety of cement types. For example, if you’re setting gate posts, purchase an anchoring cement. If you’re laying a patio or a driveway, opt for a fiber reinforced cement.
- If you are using the cement for a variety of projects or are not familiar with using cement, purchase either a regular (multi-purpose) or fast-setting mix (like Quikrete).
- Consult the sales staff at the hardware store for additional help selecting a type of cement or concrete.
- 2 Purchase cement with aggregate if you’re laying thicker concrete. If you are laying a single layer of concrete that will be thicker than 3 ⁄ 4 inch (1.9 cm)—such as a building foundation or driveway—purchase cement with aggregate mixed in. Aggregate is stones and gravel added to the cement mixture to make it stronger and less likely to crack.
- If you prefer not to buy cement with aggregate already included, you can also purchase gravel at a hardware store and add this into the aggregate-free cement later.
- 3 Put on two layers of hand protection. Cement is messy, and it will likely get all over your hands. If cement contacts your skin directly, brush it off immediately. To protect your hands, first put on a pair of latex gloves. Then, over these, put on a pair of sturdy work gloves.
- To protect your eyes, you should also always wear a pair of safety goggles when working with cement.
- Since cement will harm your lungs, think about wearing a surgeon’s mask or bandana over your mouth when pouring dry cement.
- 4 Cut open the bag of cement and empty the contents in a wheelbarrow. Use the blade of your shovel to stab an opening in the bag near one end. Then grab the cement bag firmly by the other end, and upend it so the powder spills out into the wheelbarrow.
- If you prefer to use a machine mixer rather than mixing by hand, you’ll pour the opened bag of cement into the machine basin.
- Avoid shaking the bag as your pour out the cement powder. It’s very dusty, and shaking the bag will fill the air with cement powder.
- 5 Add water to the cement powder. Using a garden hose, add a reasonable amount of water to the center of the dry cement powder. Start by adding about 1 gallon (3.8 L) of water. It’s best to start out with a smaller amount of water and add more as needed—it’s inconvenient to add a second bag of cement if you add to much water to the first batch.
- If you’re mixing multiple bags of cement, you’ll quickly get the hang of how much water is necessary.
EXPERT TIP Gerber Ortiz-Vega is a Masonry Specialist and the Founder of GO Masonry LLC, a masonry company based in Northern Virginia. Gerber specializes in providing brick and stone laying services, concrete installations, and masonry repairs. Gerber has over four years of experience running GO Masonry and over ten years of general masonry work experience. Expert Trick: If you’re working on a project where you’ll have a concrete finish, measure out 3 parts concrete, then add 1 part water. If you’re making a concrete foundation for a retaining wall or a post, the concrete can be a little more wet, because the finish won’t matter as much.
- 6 Mix the water into the cement powder. Use your shovel to stir the water into the dry powder. Pull the dry cement mix from the outer edge of the wheelbarrow into the wet center, and stir until there is no dry powder left in the wheelbarrow. Ideally, the cement should be a little runny at this point, about the consistency of thin putty.
- Stir slowly, so that the water doesn’t slosh over the sides of the wheelbarrow.
- If you’re using the mixing machine, simply flip the “On” switch and let the machine stir for you.
- 7 Add a shovel-full of sand if required. Most fast-setting bags of concrete mix will already contain sand, so you won’t need to add any. If you purchased cement without sand already mixed in, add 3 or 4 shovels-full of sand to the soupy concrete mixture, then stir until the sand has been worked in.
- The technically correct ratio of mixing cement with sand is 1 part cement, 3 parts sand, and 3 parts water. However, you can customize this ratio as you see fit.
- For most projects, you won’t need 3 times as much sand as cement. Start with a 1:1 ratio instead.
- If you’re planning to add aggregate to your concrete mixture, add the aggregate now as well. Add sand and aggregate separately to ensure that each gets fully mixed into the wet concrete.
- 1 Gather thick, clay-rich mud. If you are located near a river, lake, or other body of water, you can gather mud from its banks. Otherwise, you may need to make your own mud by digging up clay-rich soil and adding water to it. The clay should be a thin consistency so that it will mix well with dry grass.
- A clay-rich mud or soil will result in a strong, durable cement.
- 2 Gather an armload of dry grass. Walk to a nearby field or riverbank and pull up a large armload of old, dead grass. You’ll use this to mix with the mud.
- Green grass will not work. The grass needs to be dry and hard in order to make suitable survival cement.
- 3 Cut the grass to a usable length. The grass that you’ve harvested will probably be very long, which will prevent it from mixing well with the cement. Solve this problem by using a field knife to cut the grass down into a suitable length. It will be most convenient if you do this on top of a large tarp.
- For most projects, the grass will work best when cut into sections between 6 inches (15 cm) and 12 inches (30 cm).
- 4 Pour the mud out on the tarp. Do this near the location where you’ve set the cut grass stalks. Once the mud is on the tarp, set about half of the grass on top of the mud.
- 5 Stomp the mud and grass together. Either wearing shoes that you don’t mind getting muddy, or barefoot, step up and down on top of the mud and grass mixture until the two elements have been fully smashed together.
- If you don’t want to get your shoes or feet dirty, fold a corner of the tarp on top of the mud and grass and stomp on top of that.
- 6 Roll the mud and grass back on itself. At this point, the mud and grass will be smashed into a flat layer. Pick up one edge of the tarp, and lift until the mud/grass mixture folds back over itself. Do this a couple of times, until the mixture is roughly in a round shape.
- 7 Add the rest of the grass and stomp again. Place the remaining half of the dry grass stalks on top of the mud and grass mixture. Walk in place on top of the mixture, using the same technique as before. This will force all of the newly-added grass to fully blend with the mud/grass mixture, leaving you with well-blended survival cement.
- At this point, your survival cement is finished. Begin shaping and working with it immediately, as the mud will dry quickly.
- You can form your batch of survival cement into a series of bricks, which can be built into a small hut in adverse survival conditions. In non-survival situations, you could use these cement bricks to build a retaining wall or fire pit.
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- 40-pound bag of cement
- Mixing basin or wheelbarrow
- Hose for water
- Sand (optional)
- Aggregate (optional)
- Latex gloves
- Work gloves
- Safety goggles (optional)
- Mouth protection (optional)
- Commercial cement is a mixture of limestone and oyster shells (along with a blend of other shell types) that has been superheated to remove the carbon dioxide.
- Both sand and aggregate mixture can be purchased at a large hardware store, a home-supply store, or a landscaping-supply store.
Concrete can stain or stiffen any clothing that it comes in contact with, especially if it’s allowed to dry. When making concrete, be sure to wear clothing that you don’t care about.
Advertisement Article Summary X To make cement from scratch, buy or collect limestone and break it into 2 inch chunks. Put the chunks into a kiln, set the kiln to 900 °C, and let the limestone bake for 4-5 hours. Be sure to wear a respirator when you pull out the limestone, then let it cool completely.