Effects Of Rice Husk Ash/Silica Fume And Rubber Powder On Properties Of Cement Mortar

Ordinary concrete is often difficult to adapt to a variety of complex environments due to its poor durability.For the concrete engineering in some cold areas of northern China,it is quite important to improve the frost resistance and the chloride penetration resistance.In this article,rice husk ash with high pozzolanic activity was prepared via a temperature-controlled calcination of raw rice husks at 600°C and then ground.The relationship between the replacing rate of rice husk ash to silica fume,the rubber powder contents and the compressive strength,flexural strength,the frost resistance and the chloride penetration resistance of cement mortar were analyzed using the quick frost method,the electric flux method and basic mechanics method.In addition,an index R was used to evaluate the combination property of the chloride penetration resistance and the frost resistance of cement mortar.Microscopic observation of cement mortar was also carried out.The results of the study are as follows:(1)The frost resistance of cement mortar was obviously improved after adding rubber powder.Within the range of rubber content in this experiment,the frost resistance of cement mortar was better with increasing amounts of the rubber powder.after 220 freeze-thaw cycles,the mass loss rate and the relative dynamic elastic modulus of the test group with rubber powder content of 8% were reduced by 43.6% and 28.8% respectively compared with the reference group.Moreover,the chloride penetration resistance of cement mortar was better with increasing amounts of the rubber powder,the total electric flux after 6h of the experimental group with rubber powder content of 8% was 35.7% lower than that of the reference group.However,the addition of rubber powder obviously reduced the compressive a nd flexural strength of cement mortar,when the rubber content reaches to 8%,the compressive strength and flexural strength of the cement mortar reduced by 51.8% and 34.1% respectively after 28 days of curing.In addition,the effect of rubber powder on the flexural strength of cement mortar was smaller than that of the compressive strength.(2)The frost resistance of cement mortar was obviously improved after replacing silica fume with rice husk ash.When the replacement ratio reached to 100%,the mass loss rate and the relative dynamic elastic modulus were 29.8% and 21.4% lower than the reference group with the replacement ratio of 0%,respectively,which means the frost resistance was best.And when the substitution ratio was 25% and 100%,the electric flux of 6h was reduced by 5.4% and 4.5% respectively,compared with the baseline group with the substitution ratio of 0%,which means better chloride penetration resistance.In addition,replacing silica fume with rice husk ash slightly improved the compressive strength and flexural strength of cement mortar,when the replacement ratio reached to 100%,the compressive strength and flexural strength increased by 15.4% and 16.0% respectively compared with the reference group after 28 days of curing.(3)A parameter R was used to evaluate the combination property of chloride and frost resistance of cement mortar.Within the range of rubber content in this experiment,the parameter R increased with the increasing of rubber powder content,which means better combination property.Moreover,the parameter R increased firstly and then keep stable with the increasing replacement rate of rice husk ash to silica fume,indicated the combination property increased firstly and then keep stable,in other words,controlling substitution ratio above 50% obviously improved the combination property.(4)Microscopic analysis showed that the rubber powder introduced a lot of closed tiny bubbles into the cement mortar,which was a very important factor that rubber powder affected various properties of cement mortar.