# Bricks Using Clay Mixed with Powder and Ashes from Lignocellulosic Biomass: A Review
## 6 Unfired Clay Bricks Reinforced by Lignocellulosic Biomass Ash
As a result, the formula with 15% to 20% of RHA increases the compressive strength significantly when compared to the cement alone, while above this value range, the resistance significantly decreases. In the same way, [PERSON]. [80] considered a combination of lime, cement, and SBA for stabilizing the compacted soil blocks. The mixture was designated as NA, CAL, CEM,and CALBA, which refer to the compacted soil blocks, respectively, when it contained no additives, 10%, lime, 10% cement, and a combination of 10% lime and 10% sugarcane bagasse ash (SBA). Results of compressive strength tests show that adding cement and lime to the clay matrix increased the clay matrix's compressive strength. The cement mixture (CEM) showed a compressive strength of 12.7 MPa, while the lime mixture (CAL) showed a strength of 5.55 MPa. When SBA is added to lime in an equal amount (CALBA), the compressive strength increases by almost 40% and is measured at 7.7 MPa. This growth of compressive strength could be attributed to the progressive densification of the clay matrix and more precisely to hydration and pozzolanic reactions. For his part, [PERSON]. [81] calculated the amount of lime required to stabilize the soil using the pH method developed by [82]. The optimal initial lime was found to be 6%. Moreover, he concluded that the stabilization could be achieved with three different sugarcane bagasse ash (BA) contents; 4%, 6%, and 8%, respectively. For this, a linear relationship between compressive strength and the percentage of BA was found, which was supported by a fit with a regression factor R\({}^{2}\) = 0.94. By adding 8% BA, this strength increased from 1.687 MPa to 1.87 MPa, or by almost 11%. Ref. [82] investigated the possibility of using lime and rice husk (RHA) for the development of new unfired brick or compressed stabilized earth (CSE) forms. To reduce the effect of shrinkage, clay as the matrix material of the brick was mixed with sand. A standard Proctor compaction test of soil and sand mixture was performed to obtain an optimal value of the sand used according to their compaction characteristics. Thus, a maximum dry density value among the test mixture was obtained for a 70% soil-30% sand mixture. The amount of lime required for stabilization (LRS) was determined according to the method developed by [82]. Accordingly, 5% lime was found to be the optimum amount of lime to stabilize the tested soil-sand mixtures. The ratio of lime and RHA was selected as 1:1 (5%:5%); 1:2 (5%:10%), 1:3 (5%:15%), 2:1 (10%:5%). It was observed that the addition of lime and RHA increases the compressive strength. This strength reaches a maximum value of 15.5 MPa and 16.1 MPa with a lime/RHA ratio of 1:1 for the treated clay sample and the treated clay /sand mixture sample, respectively. After this limit, the compressive strength decreases. The reason for the improved performance of clay mixed with sand is that the finer particles of clay will fill the voids of the coarser particles of sand. This would result in denser, stronger, waterproof soil mixtures which result in a decrease in water absorption. The BIS specification in IS 1725 (BIS 1982) provides for two classes of stabilized blocks, namely class 20 with a minimum allowable strength of 1.96 MPa and class 30 with a minimum allowable strength of 2.94 MPa [83]. The ideal mechanical strength for each of the aforementioned studies is depicted in Figure 8.  
Figure 8: Compressive strength for unfired clay bricks stabilized with lignocellulosic biomass ash and lime/Cement: 10% OPC–8% SBA [77], 4% OPC–8% SBA [77], 12% CP–8% BA [78], 4% Cement–15% RHA [79], 10% lime–10% SCBA [80], 6% lime–8% BA [81], 5% lime–5% RHA [84]. The compressive strengths of all unfired clay bricks stabilized by the addition of cement/line with lignocellulosic ash percentages, as shown in Figure 8, are higher than those of class 30, except for the study [81], where the strength corresponding to 6% lime stabilized mud block was insufficient to meet the minimum requirements of a class 20 block.