Effect of rice husk ash particle size on alkali silica reaction risk of cement mortar
Solid waste recycling is an important part of achieving sustainable development.Rice husk ash has high pozzolanic activity and is expected to be used as an auxiliary cementitious material for cement mortar or concrete.However,the content of K2O and Na2O in RHA is high,so it is necessary to find out the risk of alkali silica reaction that may be caused by the mixing of RHA with different particle sizes.The existing research shows that the pozzolanic activity of fly ash inhibits alkali silica reaction and has been widely used.For comparison,a benchmark group,a group with 4 different particle sizes of fly ash,and a group with rice husk ash are set up.On the basis of testing the compressive strength and flexural strength respectively,the expansion rate is tested,and the microstructure and elemental composition of the rice husk ash specimens with a particle size of 5 μm and the specimens without rice husk ash are tested by SEM and EDS.The test results show that the mechanical properties of mortar can be improved by adding rice husk ash or fly ash.The smaller the particle size of rice husk ash,the greater the degree of improvement.The RHA with a median particle size of 5 μm can increase the 28 d compressive strength of mortar by 50.6％and 64.7％,both of which are better than fly ash.When the particle size of RHA is not more than 15 μm,it can significantly inhibit the expansion rate of mortar,and the inhibition effect is better than that of fly ash.5 μm rice husk ash can reduce the 14 d expansion rate by 90％,and make the aggregate harmless,while 8-20 μm fly ash only reduces the 14 d expansion rate by 60％,and the aggregate is still harmful.The pozzolastic activity of RHA can not only generate C-S-H gel with low Ca/Si ratio and reduce alkali content,but also improve the compactness of mortar and inhibit the penetration of alkali ions and water,thus showing an inhibitory effect on alkali silicate reaction.
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