# Bricks Using Clay Mixed with Powder and Ashes from Lignocellulosic Biomass: A Review
## 4 Investigation of Hybrid Bricks by Blending Clay with Ash from Lignocellulosic Biomass Combustion
### Hybrid-Fired Bricks by Blending Clay with Lignocellulosic Biomass Ash  
To study the effect of ashes on clay bricks, Table 1 summarizes several works carried out and various parameters considered during clay brick preparation. Ashes from olive wastes were the most commonly used, especially in the Mediterranean region where this ash type is produced in huge quantities. Indeed, several researchers have chosen to use these wastes as partial replacements in the manufacture of clay bricks in order to reduce the environmental effect of these ashes and to decrease the aggressive use of clay as a raw material in the ceramic industry. Ref. [60] used olive bottom ash (OPBA) from the combustion of Spanish olive pomace in a steam boiler mixed with an equal share of three types of clay: yellow, red, and black raw clay, respectively. The replacement rate was ranging from 10% to 50%. As shown in Table 2, the olive bottom ash (OPBA) was formed by 12.5% SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) which represent the skeleton components of bricks, 53.1% of melting oxides (mainly CaO, Na\({}_{2}\)O, K\({}_{2}\)O, and MgO), and gaseous components formed by 1.6% FeO\({}_{3}\), 42.28% CaCO\({}_{3}\) and 13.5% of organic matter. The latter is responsible for the generation of gases and swelling of ceramic bodies during sintering at high temperatures. The presence of significant levels of melting oxides (K\({}_{2}\)O) and auxiliary melting oxides (CaO, MgO, Na\({}_{2}\)O) in the OPBA could lower the melting point which could reduce the firing temperature. This study proves the feasibility of using OPBA up to 20% as a partial substitute for clay to produce good quality of fired bricks. However, only 10% weight of OPBA displays the optimum value that confirms the good balance provided by both melting capacity and porogen capacity. In the same context, Ref. [61] used different percentages (5%, 10%, 15%, 20%, and 25%) of fly ash from the combustion of olive pomace (CVLL) as a partial substitute for clay (black, red, and yellow). These ashes came from the same plant and same source as those used in the earlier study. 1500 tons of bottom ash and 5400 tons of fly ash were produced annually at that plant. These ashes were mainly composed of K\({}_{2}\)O, silica, and auxiliary flux oxides (CaO, MgO) (Table 2). Based on experimental results, it was shown that when using fly ash up to 25% by weight in the clay brick, the final product was useful in the manufacture of ceramic bricks for building materials. But, for obtaining bricks with superior physical and mechanical properties, a limitation of 5% by weight of CVLL should be considered. Furthermore, Ref. [62] evaluated the effect of the incorporation of olive stone ash (OSA) as a secondary raw material on clay bricks' physical, mechanical, and thermal properties. A mixture of 30% red clay, 30% yellow clay, and 40%black clay from Spain were mixed with 10%, 20%, and 30% olive stone ash by weight. As demonstrated in the study, the incorporation of 10% weight of olive stone ash in clay bricks ensured a balance between bulk density, bulk porosity, water absorption, and tensile strength. Ref. [63] incorporated various industrial wastes into clay to produce fired bricks. Sugar bagasse ash (B) and oil mill wastewater (OMW) were used at a 2.5% and 6.5% content, respectively. OMW and B act as porous agents, reducing the thermal conductivity of clay during the firing process. Ash from rice husks and sugarcane bagasse were also frequently used in the production of clay bricks. In fact, Refs. [31; 32] used leftover rice husk ash (RHA) to make clay bricks with contents of 0%, 2%, 4%, 6%, 8%, and 10%, respectively. Ref. [64] developed clay bricks with different levels of clay replacement ranging from 0% to 20% with rice husk ash. Ref. [31] showed that 4% by weight was the optimum amount of RHA waste that can be used for improving the structural, thermal, and acoustic characteristics of clay bricks. Ref.