Characteristics of Masonry Blocks Manufactured with Rice Husk Ash (RHA) and Lime

Abstract

Rice husk is one of major agro-waste material in Sri Lanka. Rice Husk Ash (RHA) is produced by burning Rice husk as fuel in brick kiln. Rice husk ash produced by burning at high temperature contains pozzolanic constituents. In Sri Lanka, cement is extensively used to manufacture masonry blocks, although the cost of cement is high. Because of having highly pozzolanic constituents in RHA, it can be used as a building material, instead of cement, to produce cement sand masonry blocks. It was frequently reported that compressive strength of RHA based blocks increases with increasing the RHA content up to 5% and further addition of RHA causes to decrease in compressive strength. In this study, an attempt is made to increase the utilization of RHA by adding Ca 2+ to the mixture. Solid masonry blocks, having the size of 360 mm x 100 mm x 170 mm, were cast with the mix proportion of 1:6 Cement-Sand. Blocks were manufactured in two series. In the first series, RHA was used as addition with respect to weight of cement. In this series, four different RHA contents (i.e., 0%, 5%, 10%, and 15%) were used with constant lime content (10%). In the second series, RHA was used as partial replacement for cement with four different RHA contents (i.e., 5%, 10%, 15% and 20%) with constant lime content (10%).The blocks were tested for 7, 14 and 28 Day compressive strength. With the presence of lime (10%), the optimum 28 Day compressive strength was found at the level of 10 % RHA. When RHA was used as addition, the optimum 28 Day average compressive strength of block was found as 4.937 N/mm 2. When RHA was used as partial replacement for cement, 28 Day average compressive strength of block was found as 3.467 N/mm 2. Thermal performances of the RHA lime based blocks were also investigated. It was found that thermal conductivity of RHA lime based block was lower compared with that of the conventional block. The RHA lime based blocks showed better structural and thermal performances. Increased use of RHA will reduce the unit cost of masonry block while improving sustainability.

Suitability of Rice Husk Ash (RHA) with lime as a soil stabilizer in geotechnical applications

“…The temperature was within the ideal value (i.e. 500 °C to 700 °C) [10] for producing an ash with high pozzolanic activity. According to the Table 3, RHA sample contains total amount of 93% of silica, aluminium oxide and iron oxides which are compounds that attribute to pozzolanic reaction.…”

“…Rice husk contains about 75% organic volatile matter and the balance 25% becomes ash which is known as Rice Husk Ash (RHA) during the burning process [2,15] and [16], that is commonly dumped as waste materials. RHA has been categorized under pozzolana, as it comprised of nearly 85-92% silica and about 3.0% and 1.0% aluminium oxide and iron oxides respectively, which are compounds that attribute to pozzolanic reaction [4,8] and [10]. The silica is in the form of amorphous (non-crystalline silica) and the ash contains higher surface area that are associated with high pozzolanic reactivity [1] and [14].…”

“…The burning temperature of the risk husk should be maintained in between 500 to 700 °C in order to produce RHA with high pozzalonic activity [6]. RHA is used as fuel for brick burning process and the temperature varies from 550 to 750 °C within the brick kiln [10]. With the presence of Ca(OH) 2 , the SiO 2 and Al 2 O 3 react with dissolved Ca 2+ and OH − and produce secondary cementitious product called "Tobermorite gel" [10] (Calcium Silicate Hydrate (C-S-H) and Calcium Aluminates Hydrate (C-A-H)).…”

“…RHA is used as fuel for brick burning process and the temperature varies from 550 to 750 °C within the brick kiln [10]. With the presence of Ca(OH) 2 , the SiO 2 and Al 2 O 3 react with dissolved Ca 2+ and OH − and produce secondary cementitious product called "Tobermorite gel" [10] (Calcium Silicate Hydrate (C-S-H) and Calcium Aluminates Hydrate (C-A-H)). It was observed that the Ca 2+ in the lime react with SiO 2 in the RHA with the presence of moisture and improve the strength of the paste [13] and [19].…”

Optimum Level of Partial Replacement of Cement with Ground Rice Husk Ash (GRHA) in Concrete

“…The study on characteristics of masonry block manufactured with Rice Husk Ash and lime [15] investigated potential use of RHA with lime to manufacture masonry blocks. Compressive strength, water absorption and thermal performance of blocks manufactured with RHA and lime have been investigated.…”