During the study of dry mixed mortar, more attention is paid on admixtures and fiber materials, while the roles of aggregate and filler are often ignored.
The effect of reasonable combination of aggregates and fillers is often beyond the reach of admixtures. Reasonable gradation can save cost and improve the comprehensive performance of the product. Experiments show that the higher amount of additives used does not mean the higher work performance, especially in the compressive strength which on the contrary shows a downward trend. To improve the compressive strength can only be solved by a reasonable cement-sand ratio.
In dry mixed mortar, aggregate is an irreplaceable component in dry mix mortar-
1). Aggregate is the biggest component in dry mix mortar products.
2). Aggregate has the properties that other components do not possess.
3). Aggregate has better volume stability and higher strength.
4). The function f other components can be effected by the properties of aggregates.
In general, aggregate has high strength, and the particles with high strength in the hardened mortar play a role of skeleton. When mortar is stressed, aggregate bears a large load, so the mechanical properties of aggregate are important to the mechanical properties of dry mixed mortar.
The volume stability of aggregate is much higher than that of cement slurry. Cement is mainly responsible for dry shrinkage and wet expansion in hardened mortar, while aggregate is relatively stable and can also play a role in limiting the deformation of dry shrinkage and wet expansion.
The dry shrinkage and temperature deformation of hardened mortar are two crucial reasons for cement mortar cracking. When aggregate gradation is not fit, the larger porosity and small fineness modulus of slurry, the higher water demand it is. Thus cause the strength of the mortar is reduced, or makes the mortar dry shrinkage deformation and temperature deformation increases, resulting in a decline in crack resistance.
By increasing the addition of redispersible polymer powder and fiber material, crack resistance of hardened mortar can be improved, but this will greatly increase the cost on the other hand. Therefore, good gradation proportion of cementitious material, aggregate, filler and appropriate additives, can prepare dry mix mortar products with excellent performance and reasonable cost.