Fly ash is the remaining ash content after pulverized coal Combustion in the power plant and belongs to industrial wastes. Fly ash is a mechanical mixture of various particles, of which most are spherical glass body, and has a larger specific surface area. Its mineral compositions are mainly glass phase, mullite, quartz, hematite, magnetite and a small amount of unburned carbon particles. By its morphological, pozzolanic and micro-aggregate effects, fly ash can increase the water retention, plasticity and long-term strength of mortar, also save cement and lime, and reduce material costs. Adding fly lash into mortar can not only reduce costs, but also improve the workability of the mortar. Adding fly ash to replace part of cement can play a role in filling and compaction. In addition, fly ash has a certain activity, can produce secondary reactions with hydration products of cement and improve the strength of mortar.
The traditional building mortar is divided into cement mortar and composite mortar. The composite mortar uses cement and lime putty as cementitious materials. Its advantages are soft mortar, good water retention and easy construction, while its disadvantages are poor water resistance, great shrinkage, low bond strength and poor durability. The basically used in current construction projects is cement mortar. Currently the exterior painting also mostly uses cement mortar. But cement mortar has its own deficiencies. Due to lack of water-retaining and thickening components in cement mortar, mortar is poor in water retention and large in layering degree, namely poor in mortar workability and great in bleeding rate, as well as higher in the amount of cement, fast in the hardening of mortar and easy to crack. The rational use of fly ash in building mortar has not only improved the workability of building mortar, but also produced no adverse effects on other use performance of building mortar. Tests have shown that adding an appropriate amount of fly ash into building mortar plays a big role in improving the workability of the mortar.
In ready-mixed mortar, fly ash or other mineral admixtures can be added. For fly ash, dry-discharged fly ash is generally used. The quality requirements of fly ash are equivalent to the technical requirements of fly ash for concrete. In the use of high calcium fly ash, pay close attention to the fluctuations of free calcium oxide content in high calcium ash and strengthen the detection to prevent high content of free calcium oxide and undermining the volume stability of cement stone in mortar. Ready-mixed mortar can also use other mineral admixtures such as slag powder and silica fume.
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