The concrete mixing ratio is a building concept comprised of four basic materials - cement sand, coarse aggregate and water.
The most common concrete ratio mix for household use is generally the 1:2:3 method,1 part cement, 2 parts sand and 3 parts fine aggregate. Cement is usually the most expensive of the three components of concrete and generally makes up slightly less than half of the total material cost of a typical concrete mix. The sand is next in cost, but more significantly, it represents about 75% (by volume) of all aggregate used in home mixtures. The gravel or coarse aggregates fills out the rest. Mix proportions are measured by weight, not volume, so metric conversions can be helpful when doing your own calculations at home with commercially sold sacks of cement and masonry products. The standard ratio when mixing concrete for the 1:2:3 mix is approximately:
1 part cement.
2 parts washed silica sand.
3 parts coarse aggregate.
The amount of water required for consistency and durable concrete mix follow the cement manufacturer's instructions.
Aggregate is the finest part of the mix and can consist of crushed stone or gravel. Stone aggregate is usually more expensive than crushed concrete or brick/block debris, but it provides a more durable surface when applied to vertical structures such as walkways and steps.Washed sand is simply sand that has been processed through a screen of some sort to remove dust and other impurities that occur naturally in most sands. This makes for a "cleaner" final mix. Less dust means less reaction between the cement paste and air (causing weak points). Even if you run your own screening station at home, we recommend buying washed rather than unwashed sand where available. A number of manufacturers offer special mixes designed for use by homeowners. These include bags of "premix", which combine the cement and sand and "stockpile" mixes, including a supply of coarse aggregate separate from the mixture.
You will find that most of these products do not follow the standard 1:2:3 ratio exactly. Instead, they are usually blended to support consistent performance in certain applications, such as parging (applying concrete over masonry surfaces) or around large rocks where you may be forced to use slightly different ratios than usual.
A few masonry suppliers offer packages with more than just three components. Some add fly ash or lime into their base powders, for example. In contrast, others sell special curing agents intended to solve problems associated with winter weather conditions in specific geographic areas. A number of suppliers also offer a line of additives designed to be blended with the mix to alter its properties. Items such as waterproofing, stain blockers and mildewcides are often available from cement companies and specialty masonry retailers.If you're doing a job yourself on a budget, keep in mind that many mixes designed for home use can be made by mixing your components. For example, buying a bag of ready-mix concrete involves only the cost of the material itself (after any discounts). Purchasing separate ingredients allows you to make up your own custom blend at a lower cost. Still, it does involve an additional step - measuring and mixing those individual components before they can be used. Keep this in mind when planning your purchases if time is of essence to your project.
There is no single concrete mix ratio that can be called the "strongest". What's most important is selecting high-quality cement, appropriate fine aggregate and proper water content. However, concrete mix ratios will depend on the purpose of the concrete. The concrete mix ratios determine the strength of the concrete. This fact implies that you need to properly understand your building needs so that you or your mason can apply the correct concrete mixing ratios. In practice, the construction industry has a concrete mix ratio table for reference. The guidelines in the concrete mix ratio table detail the standard concrete mix ratios. Following the cement mix ratios will help you attain various levels of hardened concrete strength. There are three categories in the concrete mixture formula. These are the nominal mix concrete category, standard concrete mix grade and the high strength concrete grades of concrete. The concrete grade ranges from M5 in the nominal concrete category to M70 in the high strength concrete grades category. In the nominal category, the concrete mixture ratio is provided. The right concrete mix ratio is achieved by concrete mix design in the standard and high strength grades. Accurate concrete mixing ratios are attained by using standard devices. The rules of thumb for concrete mixing are designed to prevent the separation of ingredients before they have been properly mixed together. In order to do this, they usually err on the side of caution - that means that it's always better to add too much water than too little because you can add more cement mix gradually. Also, note that if you are adding chemicals or admixtures to your mix (even common items like lime or fly ash), these should only be added after the initial batch has been well blended using clean tools - never dump them directly into an unmixed batch of concrete. When mixing, you should always use potable water for the best results - avoid contaminating your mix with anything that may be dirty or contain contaminants that can lead to weak points in your final product. Once thoroughly mixed in the cement mixer, you'll notice that concrete is more like clay than any other common building material (except perhaps clay brick). It's very stiff and thick at first, but it will begin softening up within an hour after mixing, depending on how much water was used in the initial mix. Water cement ratio in concreting works is critical. Adding too much water in concrete mixes results in weak concrete. Do a slump test to test if the water in the mixed concrete is in the correct proportions. You can find details of how to do a slump test online. Concrete takes several days to fully cure (depending on the ambient temperature) to hardened concrete. The curing process cannot be accelerated by additives or admixtures, typically added to improve certain desirable properties rather than "harden" the concrete.
Concrete is not just another name for cement or concrete mix. The term "concrete" refers to the finished product after all of the ingredients have been mixed together. Like yeast in bread-making or cheese in pizza-making, cement is an ingredient added to concrete that serves two purposes: it allows the finished material to harden by reacting with water, and it strengthens the final product by binding together loose particles within it. Cement itself is a fine powder made from limestone (calcium carbonate) and clay (silica), combined with other trace elements (such as iron oxide) to alter its properties. During the chemical reaction that takes place when water is added to cement, both calcium and silica are converted into compounds with different chemistries - this process forms crystals of calcium silicate hydrate (C-S-H—a primary component of concrete) within the concrete mixture.
The speed at which concrete sets is related to the amount of water used in the initial mix - more water, slower set. It can vary from several minutes to several hours depending on conditions, but typically it will be touchable within half an hour of mixing and fully cured within a day of mixing (depending on temperature, humidity and other factors). For projects where the concrete is being used to anchor something in place (such as a fence post), you can speed up the process by adding "accelerators" such as calcium chloride or sodium hydroxide. Keep in mind that these chemicals can degrade your finished product if too much is added, so be sure to follow the recommendations carefully.
Curing refers to all aspects of protecting new concrete during its first few days after being poured. It's essential to keep the concrete moist during this time by spraying it with water regularly. You should always avoid walking on newly poured concrete for at least three days - after that point, it can typically support your weight without impacting its ability to cure correctly.
Once cured, you'll notice that the top layer of the material has a dusting of fine white powder that comes from within - this is actually a sign of an effective cure. There are no adverse effects to be found from leaving it there after the concrete has fully dried.You should wait several days before parking your car on freshly poured concrete, and in fact, it's recommended that you keep foot traffic to a minimum during the first week or two after pouring. Depending on temperature and humidity, you might be able to drive over fresh concrete after one day after the mix hardens (depending on how much water was used in mixing), but for best results, let it cure for at least three days.
Keep in mind that even though the top layer may feel dry enough to walk on, there will likely still be moisture deeper within the mix - this can lead to serious damage when combined with the weight of your vehicle if you park too soon. For more information on concreting, and concrete slabs, take a look at the Australian Government's Your Home website.This tends to vary widely depending on where you live and the usage of the concrete, but in most cases, it can be assumed that concrete will remain stable for between 30 and 40 years without any major effects. Some sources claim that properly cured (and maintained) concrete can last as long as 100 years but bear in mind that these circumstances are very specific and by no means the norm.