# Evaluation of Rice Straw Ash as a Pozzolanic Addition in Cementitious Mixtures
## 2 Materials and Method
### Analysis of RSA Reactivity  
pH and electrical conductivity were assessed following the proposed methodology by [PERSON] et al. [26], consisting of monitoring CH/RSA aqueous suspensions in different proportions at a certain temperature for 7 days. For a given reaction time, lowering electrical conductivity and pH values indicate the RSA pozzolanic reaction taking place and, thus, the unsaturation of the solution in relation to calcium hydroxide. Different CH/RSA proportions were evaluated: 1/9, 2/8, 3/7, 4/6 and 5/5. To prepare suspensions, 50 mL of deionized water were placed inside a 100 mL Erlenmeyer flask, which was tightly closed and placed into thermostatic bath at 60 \({}^{\circ}\)C. Then CH was added and the suspension was maintained at 60 \({}^{\circ}\)C with shaking until the test dates. At this time, the electrical conductivity and pH values were measured (control values), and RSA was added. The sum of RSA and CH was 1 g. Data were collected for 7 days every 24 h. The employed instruments were a pH-meter Crison micropH2001 and a conductivity-meter Crison microCM2201.  
The Frattini pozzolanicity test was carried out in accordance with UNE EN 196-5 [27]. The procedure consisted of: (a) preparing 20 g of the PC/RSA mixture at 90/10, 80/20 and 75/25 mass ratios and adding 100 mL of distilled water; (b) keeping the mixture at 40 \({}^{\circ}\)C for 8 days in hermetically sealed polyethylene bottles; and (c) filtration through filter paper. The hydroxide ions (OH\({}^{-}\)) contained in the filtrate were titrated with a diluted 10\({}^{-1}\) mol\(\cdot\)L\({}^{-1}\) hydrochloric acid solution using methyl orange as an indicator. Calcium ions (Ca\({}^{2+}\)) were titrated by 0.03 mol\(\cdot\)L\({}^{-1}\) ethylenediamineetetraacetic acid (EDTA) solution using calcon as an indicator. The results were drawn in a graph indicating the concentration of Ca\({}^{2+}\) ions (in mmol\(\cdot\)L\({}^{-1}\)) vs. the concentration of OH\({}^{-}\) ion (in mmol\(\cdot\)L\({}^{-1}\)) [28].  
For the thermogravimetric analysis (TG/DTG), the 1/3 and 1/1 proportions of CH/RSA pastes were prepared and studied at 3, 7, 28 and 90 curing days at 20 \({}^{\circ}\)C. The control PC samples and PC/RSA pastes were also analyzed in the proportions of 7/3, 7.5/2.5, 8/2 and 8.5/1.5 with a water/binder ratio of 0.5, and were studied for the same curing ages as the CH/RSA mixtures. Samples were tested within a temperature range from 35 to 600 \({}^{\circ}\)C using aluminum sealed crucibles in a nitrogen atmosphere. The used equipment was Mettler Toledo a TGA 850 module.  
Given the high chloride content in RSA (see Table 1, and for the pH and electrical conductivity, Frattini and thermogravimetry tests, a sample washed with hot deionized water was analyzed to check their influence on reactivity. This sample was named RSAW.  
The influence of replacing RSA in PC mortars on flexural and compressive strength development was studied on 40 \(\times\) 40 \(\times\) 160 mm\({}^{3}\) prismatic specimens at two replacement percentages: 15% and 30%. The water/binder used was 0.5 and the sand/binder ratio was 3. The employed dose is detailed in Table 1.