The effect of different clays on PCE performance

First of all, we all know that the mud content of the sand and gravel in the raw material has a great influence on the PCE water reduction rate and slump retention type. In China, PCE shows strong sensitivity to clay minerals in many cases. There are many kinds of clays in different regions of China, and the sensitivity to PCE is also different.

Clay, a silicate mineral, mainly includes montmorillonite, kaolinite, illite and mica, etc. The difference of clay in different regions is mainly caused by the different contents of the above minerals. According to our research, the adsorption capacity of montmorillonite (referring to extremely fine debris) to PCE is much greater than that of cement. Although the five-minute initial adsorption rate of PCE by various clays is greater than that of cement, the initial adsorption rate of montmorillonite is higher than that of cement. The largest, can reach 80%, far greater than 11% of cement. Montmorillonite is a three-layer sheet structure, and the study shows that the interlayer spacing is almost the same as the size of the PCE branch chain, which is just embedded to make it expand and reduce the effective PCE. After the clay absorbs water, it also expands, causing the solid volume in the concrete mixture to increase and the liquid volume to decrease, which ultimately deteriorates the workability of the concrete.

Secondly, the water-reducing effect also depends on the amount of cement. When the amount of PCE is the same, and the amount of cement is from 330-420kg/m³, the water-reduction rate increases from 18% to 35%.

Third, the particle gradation and sand filtration of the aggregates in the concrete also affect the water reduction rate. The sand rate varies between 40% and 50%, and the water reduction rate differs by 4%.

Finally, in the mix ratio, the amount of cementitious material is insufficient or the amount of mineral powder is high, resulting in a low concrete slurry ratio, which is manifested as exposed stones and poor wrapping, but the concrete is still sticky. It is advisable to adjust the PCE modified components, such as the use of viscosity modifiers, soluble sulfates, etc., while properly adjusting the total amount of cementitious materials in the concrete mix ratio, the gradation of sand and gravel or the sand ratio, and the mix of fine and coarse sand and other measures.