Introduction

The construction material ‘cement’ composition is such that it ultimately binds the blocks and metals, more importantly, perfectly. When cement is mixed well with water, it generally forms a plastic mass known as cement paste. It is seen that when the hydration reaction occurs, products based on gel and dense crystalline material are formed. 

A compact hard rock-like material takes shape because of the interlocking of the crystals and the inert particles present in the concrete cement. Cement solidification happens in two ways. It is either by setting or by hardening the cement material. 

Setting process in cement

The solidification process comprises the thickening of the fresh or original cement paste, which is the plastic mass. An initial gel formation followed by crystallization keeps adding a definite level of hardness to the cement. As this process begins, it reflects that adequate strength is evolving because of the gradual and continued reaction between water and the particular cementitious component.

Hardening process in cement 

There is a slight difference between setting and hardening. The hardening of cement implies the development of strength because of the slow and gradual process of crystallization of the inner mass of cement. It comes into the picture soon after the cementing process is over. Concrete cement takes many months to harden. This is not a drying process and it can happen even when there is some water in the concrete.

Difference between setting and hardening cement

Setting implies stiffening of the cement paste from fluid to a rigid form of material. In this process, the concrete cement gets its shape depending on the support inside, which converts from the plastic state to the amorphous form. During the setting stage, in case the external support that helps it stays in that position is removed, there are changes of deformation or cracks that will surface. 

Hardening is the strengthening process wherein the hydration of silicate compound happens in concrete, and it acquires immense strength with time. In this case, when the hardening process is in progress, there is hardly any need for any support because the concrete gets stronger after stiffening, unlike the initial setting time. 

How does gypsum control the rate of hardening of cement?

When it comes to the hardening process of cement, gypsum plays a vital part. Gypsum is a mineral, and its chemical name is hydrated calcium sulphate. When cement is manufactured, and the clinker cools, some gypsum is added when the grinding process is nearing completion. This is generally added at the time of cement setting. This is an essential ingredient; if this is not added, the cement will harden soon after mixing with water, and there will hardly be any time for concrete placing. In this way, gypsum helps to control the rate of setting of the cement. This is a retarding agent of cement and an indispensable component.

What are the disadvantages of rapidly hardening cement?

It is seen that rapidly hardening cement can become firmer much faster than ordinary Portland cement. Although it has some advantages, like lower shrinking rate, high resistance to chemical attack, and less carbon dioxide emission, it also has some disadvantages. This is not recommended to be used for water retention in dams or dikes. Rapidly hardening cement, known as hydraulic cement, gives out lots of heat that leads to hydration. The speed at which this process occurs because of a huge volume of water can cause cracks and later rust that retards the life of any concrete structure. This should never be used in the mass concreting process of large-sized concrete structures. The rapidly hardening cement comes costlier than other materials in the hardening cement category, so this might not be a preferred choice of many construction manufacturers.

How do they build underwater?

While venturing into a building underwater, great care must be taken to use only those materials that can withstand any amount of erosion, corrosion, and even water pressure. Concrete is commonly used in underwater construction, apart from acrylic glass and steel. There are four different methods to build underwater. Caissons are watertight structures that can go deep in the water by maintaining a dry environment. Cofferdams are short-term enclosures allowing water to be pushed out and create a dry space within for construction. Off-site buildings are constructed by floating the parts and assembling them before lowering them into water. Then there are driven piles that allow crews to make durable structures without even gushing out the water. Using the best ways helps to ensure that the cement is set and hardened to keep the structures solid and steady.