cementpaste

Cement paste is the binding matrix formed when Portland cement is mixed with water. It binds aggregates in concrete and serves as the mortar or grout base in construction. In concrete, cement paste surrounds and coats aggregate particles, filling voids and transmitting loads as the mixture hydrates and hardens.

Chemically, cement paste develops through hydration reactions. The primary products are calcium silicate hydrate (C-S-H) gel and calcium hydroxide, which progressively build a rigid network that gains strength over time. The water-to-cement ratio influences workability, setting time, porosity, and strength: higher ratios improve plasticity but increase porosity and reduce long-term strength, while lower ratios yield stronger, denser paste but harder workability. Additives such as superplasticizers, accelerators, retarders, or air-entraining agents modify rheology, curing, and durability.

In its fresh state, cement paste is a viscous, plastic material that can be shaped and placed around aggregates. During curing, the hydration reactions release heat and gradually transform the paste into a hardened solid. Proper curing—maintaining adequate moisture and temperature—enhances develop­ment of strength and durability. The microstructure features gel and capillary pores; pore size distribution affects permeability, shrinkage, and resistance to chemicals and freeze–thaw cycles.

Applications center on its role as the binding phase in concrete and mortar. Cement paste properties are critical to overall performance, influencing early strength, long-term durability, and service life. Environmental considerations note that cement production is energy-intensive and a significant source of CO2 emissions, motivating research into alternative binders and more efficient formulations.