Effectiveness of zeolite powder as an auxiliary cementing material for concrete

Natural zeolite is a silica-alumina material with skeletal structure, which is usually used as an auxiliary cementing material for cement and concrete. 2018, the Ministry of Housing and Urban-Rural Development published the industry standard "Natural zeolite powder for cement and mortar", which stipulates that zeolite material should be used as a component of concrete. And relevant researchers have also shown through experiments that the mixture with zeolite powder has good cohesion, not easy to seepage and segregation, and the structure of zeolite powder concrete is more dense, water absorption and chloride ion permeability coefficient is greatly reduced, the resistivity can be significantly increased. 

In addition, some scholars have proved through tests that the addition of 10-20% zeolite powder can effectively control the harmful expansion caused by alkali-aggregate reaction, which indicates that zeolite powder concrete has better durability, so it is worth promoting and applying.

zeolite powder can be added to the concrete auxiliary

With more and more construction projects in China, the price of auxiliary cementing materials such as silica fume, slag and fly ash is getting higher and higher. Zeolite powder is a volcanic ash material formed by grinding natural zeolite rocks, which has a large internal and external specific surface area (3545m2/g) and contains a large amount of active SiO2 and Al2O3, which can release Ca(OH)2 from cement hydration. the reaction can generate more CSH gel and hydrated aluminate, which can improve the microstructure of hardened cement paste and improve the building strength and quality.

Although most volcanic ash materials (silica fume, fly ash, etc.) are glassy or amorphous, natural zeolites with crystalline structure are of higher quality than fly ash and slag due to their also volcanic ash nature and their volcanic ash activity which is second only to silica fume. Numerous data show that zeolite powder can improve the viscosity of concrete, thus eliminating segregation and bleeding. Through the filling effect of zeolite powder and volcanic ash reaction, it can reduce the total porosity of concrete and improve the interfacial transformation between cement paste and aggregate, which greatly improves the mechanical properties of concrete.

experimental process and results

The cement used in the experiment was PII42.5 silicate cement produced by a cement plant, whose strengths were 29MPa and 51MPa at 3 and 28 days, respectively. the mixture used natural zeolite powder (zeolite content over 90%) produced by a company, silica fume produced by a company and secondary fly ash produced by a power plant.

The zeolite powder was substituted for 5%, 10%, 15% and 20% of the cement, respectively. When the same slump (170 mm) was achieved, the water reducing agent content used for zeolite powder concrete was higher than that of the reference sample and silica fume concrete, and the content of water reducing agent used for zeolite powder concrete increased greatly with the increase of zeolite powder content. 

Compared with the reference sample, the air content of zeolite powder concrete was higher and gradually increased as the zeolite powder content increased due to the porous framework structure and huge internal specific surface area of this zeolite powder, which could adsorb more mixed water and additives, even higher than the adsorption capacity of silica powder. Therefore, this zeolite powder concrete requires a large amount of water, it has good cohesion, high air content, and does not bleed out and segregate easily, so it is very suitable for the preparation of pumped concrete.

Because of its porous framework structure and huge internal specific surface area, zeolite powder can absorb large amounts of mixed water and additives, resulting in a zeolite powder concrete with a high water requirement, a slightly higher air content, and good cohesion in its Mixture. In addition, the addition of 10-20% zeolite powder can effectively control the harmful swelling caused by alkali-aggregate reaction through adsorption, ion exchange and secondary hydration of zeolite powder.