The question we are asked most often is “What are Zeolites and why do you use them in your range of cement modification products?”
The simple answer is because they work, the longer answer is that we have over 25 years experience with zeolites. It is essential that the right type and the correct dosage is used for each product/application.
Zeolites are hydrated alumina-silica-based minerals that have three-dimensional crystalline frame structures with alkali and alkaline earth cations. Zeolites can absorb and desorb water due to high porosity of up to 30%.
The superior contents of silica present in zeolites reacts with Ca(OH)2 from the Portland cement system and produces an additional phase of calcium silicate hydrate (C-S-H). C–S–H is typically a density increasing and strength-giving substance in the Portland cement system leading to an improved microstructure.
For mechanical properties, whilst little additional compressive strength is usually found for zeolite modified specimens compared to cement alone samples, there a noticeable increase in strength at the later ages in 180 days.
Zeolites can provide a good contribution to preventing alkali-silica aggregate reaction (ASR) by decreasing the alkaline ion concentration in the pore solution of concrete through cation exchange i.e., absorbing the alkalis and releasing the calcium.
Zeolites also increase the electrical (surface) resistivity of the concrete by reducing the ionic concentration, and pore size.
Zeolites absorb a part of the mixing water in the fresh state of concrete, and later this same water migrates during the hardening state which eventually leads to a decrease in drying shrinkage.
Zeolites can actually reduce the workability of cementitious mixtures as the water demand is higher due to the larger available surface area of the particles, adding additional water during mixing should not cause any reduction in strength nor any significant reduction on setting time.