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  • River sand was graded in accordance with ASTM C


    River sand was graded in accordance with ASTM C778 [47] (see Table 2). The graded sand had a water PF-06447475 of 1.00%, fineness modulus of 3.49 and specific gravity of 2350kg/m3. A polycarboxylate based superplasticizer called ZP with pH of 7±1 and specific gravity of 1.1±0.02 was also used to adjust the desirable flow. Potable water was used for both curing and casting purposes.
    Experimental program In this study, eight different mortar mixtures were prepared by water/binder ratio of 0.46 and sand/binder ratio of 2.18. The proportion of mixtures containing NRHA and MRHA are presented in Table 3. The preparation procedure involved: After casting, wet towels were used to cover specimens for 24h in order to prevent excessive water evaporation. For curing, the mortar specimens were demolded and placed in water (saturated with calcium-hydroxide) at 23±2°C until the test day.
    Testing methods
    Results and discussion
    Conclusions In this paper, the effect of nano and micro rice husk ash on the development of compressive strength, capillary absorption electrical and chloride resistivity of mortars was investigated. The following results for mortar mixtures with 0.46 water/binder ratio and 2.18 sand/binder ratio were obtained:
    Introduction Protection of functional groups is often necessary during a multistep organic synthesis, so the development of economical and efficient methods for this purpose is very important. Hydroxyl and amino groups in alcohols, phenols and amines are often present in organic molecules, and their protection is an important process during organic reactions. Among various procedures for the protection of hydroxyl and amino groups, acetylation with acetic anhydride or acetyl chloride in the presence of an acidic or basic catalyst is an efficient and common route due to the stability of the products in acidic media and easy introduction and removal of the acetyl group. For this purpose many Brönsted and Lewis acidic catalysts have been used [1], [2], [3], [4], [5], [6]. Although these methods are improved, most of them suffer from disadvantages such as long reaction times, use of organic solvents, expensive catalysts, use of excess amounts of the acylating agents and harsh reaction conditions. Therefore there is still a need to find an alternative method which might be mild and catalytically and economically efficient. In recent years, synthesis of nanocrystalline metal oxides has attracted much attention due to their unusual catalytic properties compared to bulk metals [7]. Among various metal oxides, TiO2 nanoparticles is one of the most utilized ones which have been widely investigated as the catalyst, pigment, food coloring substance, etc [8], [9]. Preparation of the non-agglomerated TiO2 nanoparticles, with a narrow size distribution in anatase form, is very important to achieve higher catalytic activity and more readily handling than the commercial TiO2[10], [11]. On the basis of this subject, the synthesis of TiO2 over a silica support was explored as a useful way for preventing the agglomeration and formation of dispersed TiO2 aggregates [12]. Siliceous materials are desirable because they are chemically inert and have a high specific surface area and thermal stability. Rice husk, the outer covering of rice grains, is one of the main agricultural residues which is obtained during the milling process. Application of rice husk as an energy source for biomass power plants, rice mills and brick factories is increasing due to its high calorific power [13]. In this combustion, rice husk ash (RHA) is produced. RHA contains a considerable amount of amorphous silica up to 80% and small proportion of impurities such as K2O, Na2O and Fe2O3[14]. In recent years, investigation on the application of TiO2-based reagents in organic reactions became an important part of our ongoing research program [15], [16], [17]. In continuation of these studies and because that RHA possesses high silica content, we were interested to investigate the possibility of the preparation of anatase-phase TiO2 over this reagent.