The role of silica fume and fly ash in pervious concrete
Key words
Pervious concrete, silica fume, fly ash
Pervious concrete, also known as porous concrete, sandless concrete, permeable floor. It is a porous lightweight concrete made of aggregate, cement, reinforcing agent, and water, and it does not contain fine aggregate.
Permeable concrete is composed of coarse aggregate surface covered with a thin layer of cement paste and bonded to each other to form a honeycomb structure with evenly distributed pores, so it has the characteristics of air permeability, water permeability and light weight.
Fly ash contains more than 70% glass microbeads, with complete particle shape, smooth surface and dense texture. For concrete, this form can undoubtedly play the role of water reduction, densification and homogenization, promote the deflocculation of initial cement hydration, and change the rheological properties, initial structure and various functions after hardening of the mixture. , Especially for pumping concrete, it can play a good lubricating effect. The microbeads in fly ash can improve the workability of permeable concrete, so that the cementitious material can be evenly wrapped on the surface of the aggregate without segregation or bleeding.
Active effect of fly ash
Because fly ash is an artificial pozzolanic material, it is also called "pozzolanic effect". Because the chemical composition of fly ash contains a large amount of active SiO2 and Al2O3, it chemically reacts with alkaline substances such as Ca(OH)2 in a humid environment to form gelling substances such as calcium silicate hydrate and calcium aluminate hydrate. , It can enhance the fly ash products and concrete and block the capillary structure in concrete, and improve the corrosion resistance of concrete.
Micro-aggregate effect of fly ash
Microbeads and debris with small particle size in fly ash can be equivalent to unhydrated cement particles in cement stone, and extremely fine microbeads are equivalent to active nanomaterials, which can significantly improve and strengthen concrete and products. structural strength, improve homogeneity and compactness.
Silica fume can fill the voids of cement particles, making the cement stone structure of pervious concrete stronger. Silica fume can continue to react with calcium hydroxide, the hydration product of cement, to produce calcium silicate gel, thus making the structure of cement stone more compact.
