Additives increasing the strength of concrete are used to improve the mechanical properties of concrete, such as resistance to compression, stretching, abrasion or swelling. They are used to modify a concrete mix or hardened concrete. The following types of additives can be distinguished:
- mineral additives (e.g. microsilica)—due to its very small particle size, SiO2 penetrates the spaces between cement grains, filling the resulting micropores. Because of this, it increases its strength;
- cement additives (e.g. aluminous cement)—used in specialised applications, such as the production of heat-resistant products, repair of concrete under chemically aggressive conditions, or for waterproof repairs;
- chemical additives (e.g. calcium chloride)—they accelerate the setting of concrete and increase its strength;
- fibrous additives (e.g. steel fibres and polymer fibres)—they increase resistance to cracking and temperature changes;
- additives for a pozzolanic reaction (e.g. fly ash)—they cause the formation of micro-bubbles in the concrete, which increases its volume and reduces the unit weight.
