How does cement get hard

Cement and water form a paste that coats each particle of stone and sand—the aggregates. Through a chemical reaction called hydration, the cement paste hardens and gains strength. The quality of the paste determines the character of the concrete. The strength of the paste, in turn, depends on the ratio of water to cement.

The water-cement ratio is the weight of the mixing water divided by the weight of the cement. High-quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability of fresh concrete, allowing it to be properly placed, consolidated, and cured.

A properly designed mixture possesses the desired workability for the fresh concrete and the required durability and strength for the hardened concrete. Typically, a mix is about 10 to 15 percent cement, 60 to 75 percent aggregate and 15 to 20 percent water. Entrained air in many concrete mixes may also take up another 5 to 8 percent.

Almost any natural water that is drinkable and has no pronounced taste or odor may be used as mixing water for concrete. Excessive impurities in mixing water not only may affect setting time and concrete strength, but can also cause efflorescence, staining, corrosion of reinforcement, volume instability, and reduced durability.

Concrete mixture specifications usually set limits on chlorides, sulfates, alkalis, and solids in mixing water unless tests can be performed to determine the effect the impurity has on the final concrete. Although most drinking water is suitable for mixing concrete, aggregates are chosen carefully. Setting time is reduced if the weather is hot as heat speeds the chemical reaction. Generally speaking, concrete will reach a useful strength in about 3 days although this does depend on the mix design and constituent materials.

The majority of strength is gained within a month. It is important to remember that concrete will reach its maximum strength only if moisture is present during the hardening process.

In standard industrial cases, full strength concrete is recognized at 28 days. At this point the neighborhood dog will not leave his footprints in it, but you should keep it clear of heavy equipment during this time period.

Most mixes are cured at 28 days. Temperature also has an impact on concrete setting time. For more information, check out this article about how concrete curing temperature makes a difference. If you are wondering about how long concrete takes to set, a solution for your concrete setting needs is a concrete heating or cooling blanket.

But not all blankets are created equal. Consider the following two types of solutions to the effects of hot and cold:. The FluxWrap from North Slope Chillers is portable cooling equipment that will keep newly poured concrete safe from heat, regulating concrete setting time in both regular and hot conditions. The FluxWrap is combined with either a cooler or chiller to achieve optimum results. The Circulation Blanket draws heat to the blanket in order to cool the concrete. If conditions are cold, concrete curing blankets provide a manageable way to cure concrete effectively and confidently.

Powerblanket curing blankets increase production by rapidly curing with consistent, even heat. The type of blanket and how that blanket is used will have a massive impact on your concrete. Instead of dried fruit and nuts, you have sand and gravel.

And a concrete form takes the place of the cake pan. Finally, instead of the heat that bakes the cake, concrete uses water. While heat is the prime mover in getting the cake batter to change its characteristics, in the concrete mix it's water that gets things going. Perhaps the most important thing to understand about concrete is the role of water. First, it provides plasticity so the concrete can be poured in a form.

Its real importance, however, is in the hardening process. Wet concrete doesn't harden by drying. Instead, the water is a chemical component in a curing process.

The compounds that react with the water are in the portland cement. Isle Of Portland While cement in one form or another has been around for centuries, the type we use was invented in in Britain.

It was named portland cement because it looked like the stone quarried on the Isle of Portland. Portland cement is produced by mixing ground limestone, clay or shale, sand and iron ore. This mixture is heated in a rotary kiln to temperatures as high as degrees Celsius. The heating process causes the materials to break down and recombine into new compounds that can react with water in a crystallization process called hydration. Concrete cures in several stages—a factor that allows it to be trucked to the job site and still be ready to pour.

With the concrete in the form, the cement begins a slow cure and the mix hardens. After about 36 hours, most of the hydration process is complete, but the cement will continue to cure as long as water and unhydrated compounds are present.

While the process can take years, strength tests are typically done after 28 days. It's important to use the right amount of water.