EFFECT OF RICE HUSK ASH ON THE PROPERTIES OF HYDROTECHNICAL CONCRETE

Subject: operation of concrete and reinforced concrete hydraulic structures on river systems and in the extended coastal zone of Vietnam takes place under the influence of aggressive environments, which significantly limits their service life. Therefore, the search for ways to solve the problem of increasing the durability and terms of maintenance-free operation of such facilities is very important. Previous studies have established the possibility of increasing the operational performance of hydraulic concrete (HC) by modifying their structure with complex additives that combine the water-reducing and densification effects. The possibility of increasing the quality of hydraulic concretes by using rice husk ash (RHA) as a finely dispersed mineral additive with high pozzolanic activity was also established. Research objectives: modification of the structure of hydraulic concrete; determination of the effect of an organo-mineral modifier consisting of RHA in combination with a superplasticizer on water resistance, chloride-ion permeability and strength of hydraulic concrete. Materials and methods: portland cement of type CEM II 42.5 N was used with the addition of rice husk ashes and a superplasticizer ACE 388 “Sure Tec” BASF. Quartz sand and limestone crushed stone were used as aggregates. Composition of the concrete mixture, compressive strength of concretes, water resistance and permeability of the concrete structure for chloride ions was calculated based on methods of Russian and international standards. Results: the use of an organo-mineral modifier consisting of a water-reducing superplasticizer ACE 388 and finely dispersed rice husk ash leads to a densification of the HC structure, which increases their water resistance and decreases the permeability for chloride ions. Conclusions: it was found that the introduction of the developed organo-mineral additive into the concrete mixture leads to densification of the concrete structure, contributes not only to the growth of compression strength at the age of 28 days by 32 % for HC-10, 23 % for HC-20 and 9 % for HC-30, but also to the increase of its water resistance by one or two marks. In addition, there is a significant decrease in the permeability for chloride ions of HC samples containing 10, 20 and 30 % RHA by mass of the binder, since the average value of electric charge that have passed through the samples made of HC-10, HC-20 and HC-30 were 305, 367.5 and 382.7 K respectively against 2562 K for control samples made of non-modified concrete without RHA. (The experimental results of measuring permeability for chloride ions were obtained according to standard ASTM C1202-12). Our study has confirmed the assumption that the introduction into the concrete mix of organo-mineral modifier consisting of a polycarboxylate superplasticiser and fine ash of rice husk, up to 90 % consisting of amorphous silica, will increase the density of hydraulic concrete structure, which will increase their strength, water resistance and reduce permeability for chloride ions.