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  • br Results and discussion Analysis of experimental data

    2019-11-16


    Results and discussion Analysis of experimental data indicates that the radon NVP-AEE788 coefficient in OPC blended with RHA varies from 0.15 × 10−6 m2 s−1 for pure cement to 0.26 × 10−6 m2 s−1 for cement mixed with 50% RHA by weight. The value of diffusion coefficient first decreases in cement with RHA up to 30% by weight and then again increases with value of 0.04 × 10−6 m2 s−1 at 20–30% RHA. The corresponding radon diffusion lengths varies from 0.26 m to 0.34 m with minimum value of 0.13 m at 20–30% RHA (Table 1). The chemistry of RHA cement involves the chemical reactions of the amorphous silica in the ash with lime to form calcium silicate hydrates (CSH). The compounds in cement primarily are responsible for the strength. In the case of a mixture of Portland cement–rice husk ash, the silica reacts with extra lime in the Portland cement, which in some cases can be as high as 60%. The silicates formed are of the kinds: CSHI and CSHII; the reaction may be illustrated (Boateng and Skeete, 1990) as:where The type of the ash suitable for the pozzolanic activity is amorphous rather than crystalline ash. It has been established that the silica in the ash undergoes structural transformations under varied temperature conditions. When the percentage of the RHA is increased, the total porosity decreases and this decrease in the total porosity is attributed to the change occurring in the pore size distribution as a result of using RHA which could react with the calcium hydroxide to form CSH (El-Dakroury and Gasser, 2008). The calcium hydroxide released during cement hydration is consumed as a result of interaction with active amorphous silica present in the RHA to form the CSH phases, which could contribute to the increase in the compressive strength. The variation in radon diffusion coefficient with % of RHA mixed with OPC is shown in the Fig. 2.
    Acknowledgment The financial aid granted to one of the authors, A.K.Narula in the form of FIP Scheme by University Grants Commission, New Delhi, India, is thankfully acknowledged.
    Introduction Cement-based grouts are usually applied in most of geotechnical applications [1]. Jet grouting, permeation grouting, compaction grouting, coating pre-stressed cables, tunnels applications and rock pre-stressing anchors are the examples of the cement-based grout applications [2], [3], [4]. The rheological properties of the grouts are directly related with the pumpability while penetrating to voids and cracks. Cement-based grouts are called as a suspension composite of water, cement and, possibly, admixture. One of the important parameter in cement based grout is water to cement ratio (w/c). Different ranges of w/c ratios can be used for grouting applications. While doing the coating of prestressed cables, w/c ratio is ranged between 0.35 and 0.42 [5]. For the repair and consolidation of masonry structures w/c ratio of cement grout is ranged between 0.5 and 1.5 [6]. As jet grouting applications need to behave like fluid to penetrate into soil or rock, w/c ratio changes between 0.6 and 2 [7]. Sealing cement grouts should have w/c ratios between 0.5 and 1 [8]. Fig. 1 shows the schematical view of the different areas of use of cement grout and regarding of w/c ratio. Grouting applications in geotechnic are one of the most common issues [9], [10]. In grouting applications high compressive strength is not expected with compare to concrete has. For example; 1MPa compressive strength value can be supposed as higher value for stabilizing the problematic soils in geotechnical applications [11]. Therefore, small compressive strength values with compare to concrete are acceptable values for geotechnical applications. Rheological, durability, and fresh properties of cement grouts are generally improved by using chemical and mineral admixtures. Adding minerals to the grout at different compositions changes the hardened and the rheological properties of grouts. For different kinds of grout applications different additions (like fly ash, bentonite, silica fume, cement kiln dust and metakaolin) have been used [12], [13], [14], [15], [16]. As it is known in literature a few of mineral admixtures like fly ash have an increase not only in the durability but also in the workability and long-term performance of grout mixture [17]. As a result, the mineral additives using in grout applications decrease the cost of application but increase the fluidity and the long-term capacity.