Many researchers studied the experimental investigation of
Many researchers studied the experimental investigation of RHA in cement enhances the strength and durability of the concrete , , , . It is most important that concrete must withstand its strength even after it is being exposed to any corrosive environment over a period of time. In addition, concrete exhibiting good strength shows higher durability as well. Durability is the ability to resist against environmental risks and maintaining concrete desired engineering properties . The addition of RHA in cement showed that increase in mechanical strength and durability of the mortar since the pores of the mortar contains RHA . The aspects of concrete including resistance to weathering action, chemical attack, alkalinity, carbonation, freezing and thawing, abrasion dna ligase attack and chloride ingression are considered as important factors for concrete durability . One of the most challenging task for construction Industry is the deterioration of reinforced concrete structures , , . The resistance to chloride penetration of mortar and concrete is addressed as major issues for maintaining the durability of concrete structures. Chloride ions affect the durability of concrete subjected to the action of sea water, chloride-bearing air in marine areas and de-icing salts. When the chloride concentration of mortar or concrete exceeds a certain threshold value, depassivation of steel occurs and reinforced steel starts to corrode simultaneously . In another study, Prinya et al.  measured that chloride ion penetration and its diffusion coefficient for RHA blended cement mortar experimentally and found that decreasing permeability when increasing RHA replacement in cement mortar 5 and 10 wt% respectively.
In concrete, cement act as an aggregate binder and therefore it decides the quality of the concrete. Cement mainly contains lime, silica, alumina, and iron oxide. Acidic environment contains sulfuric acid which can react with free lime contained in cement and form a component of a larger volume. This process causes expansion and cracking in concrete . Currently, the environment is contaminated by incomplete combustion of fuels and various Industrial pollutants . Combustion of fuels containing sulfurous compound releases gas which further combine with moisture present in the air to form sulfuric acid. In addition, certain bacteria convert sewage into sulfuric acid. Sulfuric acid is particularly aggressive to concrete because the calcium sulfate formed from the acid reaction deteriorates concrete during sulfate attack , , . Ganesan et al.  reported that boiler feed burnt RHA contains higher pozzolanicity leads to increase the strength of the concrete and decreases its permeability. The partial replacement of RHA combined with fiber in cement exhibits significant increase of strength and decrease of permeability of concrete was reported by Hesami et al. .
Experimental programme The materials used in the present investigation were three types of Rice husk (received from Bhaba rice mills, Red Hills in Tamil Nadu, India) and its RHA. RHA was produced by uncontrolled burning of the Rice husk. The proximate analysis of Rice husk (Moisture=11.85–12.38%; Volatile matter=51.12–52.29%; Ash=20.65–22.42% and Fixed Carbon=14.58–14.61) and RHA (Moisture=7–8.23%; Volatile matter=18.32–21.13%; Ash=49.81–52.5% and Fixed Carbon=20.95–22.06%) was determined using IS 1350 standard procedure. In addition, the RHA was grounded using ball mill by varying the grinding time of 0 (un-ground), 15 and 60min. And their corresponding size was measured and used to calculate the RHA specific surface area. Cement (OPC of 53 grade; Specific gravity=3.12) and aggregates (Fine Aggregates – Specific gravity 2.6 and Absorption capacity 0.853 wt%; Coarse Aggregates – Specific gravity 2.79 and Absorption capacity 0.518 wt%) were used to make concrete mix. These properties were used to validate the experimental findings. Cement concrete specimen with RHA were made as per Indian standards, IS: 10262-1982. The grounded RHA used as cement additive was mixed with a water to binder ratio of 0.45 in order to attain a compressive strength of 25 Mpa and then casted in 150×150×150mm iron mould for compressive and 100mm in diameter and 200mm in height cylindrical moulds for splitting tensile strength respectively. The test instruments used in this investigation were muffle furnace, sieve shaker, particle size analyzer, SEM/EDX and strength testing machine. The material description, instruments design specifications and detailed experimental procedure for rice husk characterization, RHA preparation and characterization of RHA types, making and testing of cement concrete specimen with RHA are clearly explained in Alex et al. (2016) .