# Study on Preparation and Properties of Sintered Brick from Multi-Source Solid Waste
## 3 Results and Discussions  
### Influence Law of Compressive Strength  
#### 3.1.1 MGB Sintered Brick  
(1) Influence of heating rate and holding time on the mechanical properties of sintered brick.  
As shown in Figure 3, the mechanical strength of the sintered brick mixed with waste glass slag is improved, which is mainly due to the filling of the micropores of the sintered brick by the glass slag in the high-temperature molten state. When the sintered brick was sintered at a heating rate of 5 \({}^{\circ}\)C/min, the strength of the sintered brick reached 10.76 MPa, which was due to the appropriate heating rate to provide sufficient conditions for the volatilization of water vapor, CO\({}_{2}\), and other gases inside the sintered brick. The mechanical strength reached the maximum value when the heating rate was 10 \({}^{\circ}\)C/min. However, with the continuous increase of the heating rate, the strength of the sintered brick started to show a significant decrease.  
As can be seen from Figure 3, when the holding time was 90 min between temperature gradients, the short holding time was not enough to maintain the reaction conditions of the internal physicochemical changes of the sintered brick, and performance indexes such as water absorption rate and the saturation coefficient of the sintered brick did not reach the ideal degree. When the holding time was 120 min and 150 min between the temperature gradients, the physicochemical reaction and heat absorption, and the exothermic process of the sintered brick at high temperature remained stable; the degree of densification of the sintered brick was improved, and the water absorption rate was reduced and kept constant.  
Figure 3: Effect of heating rate and holding time on compressive strength of MGB sintered brick.  
Meanwhile, the saturation coefficient was reduced to the minimum value at 120 min of heat preservation. With the incorporation of 10% glass slag, the high-temperature environment showed a significant fluxing effect, and the performance of the sintered brick was further improved. In summary, after fully considering the factors of time, energy consumption, and preparation cost, the test adopted a heating rate and holding time of 10 \({}^{\circ}\)C/min and 120 min, respectively.  
(2) Effect of sintering temperature on the mechanical properties of sintered brick.  
The specimens were sintered in a ZMF-1700C-18L vacuum atmosphere chamber furnace at 950 \({}^{\circ}\)C, 1000 \({}^{\circ}\)C, 1050 \({}^{\circ}\)C, and 1100 \({}^{\circ}\)C, respectively.  
In this paper, we tested the comparative changes in the mechanical strength of sintered brick made of construction waste and sintered brick prepared by mixing construction waste with waste glass slag under different sintering temperature conditions, as shown in Figure 4. It can be seen from the figure that the strengths of the MRB and MGB sintered bricks reached 8.1 MPa, 8.19 MPa, 10.76 MPa, and 10.79 MPa at 1050 \({}^{\circ}\)C and 1100 \({}^{\circ}\)C, respectively. The strength of MRB sintered brick was still increasing after 1050 \({}^{\circ}\)C, while the strength of the MGB sintered brick did not significantly increase, which is due to the fact that the sintered brick mixed with glass slag was affected by the thermal effect of glass. The sintering temperature was reduced and the thermal stability of the sintered brick under a high-temperature environment was improved. At this stage, the crystallization or rearrangement of the amorphous structure, and the formation of mulite and other material components occurred inside the sintered brick, and the waste glass slag in the molten state combined with the unfused quartz particles to fully fill the tiny cracks inside the sintered brick and enhance the densification degree. With the increase of the maximum sintering temperature, the strength of the sintered brick was not significantly increased.