Mechanical and self-healing properties of cement paste containing incinerated sugarcane filter cake and Lysinibacillus sp. WH bacteria

Cement is the most widely used construction material due to its strength and affordability, but its production is energy intensive. Thus, the need to replace cement with widely available waste material such as incinerated black filter cake (IBFC) in order to reduce energy consumption and the associated CO2 emissions. However, because IBFC is a newly discovered cement replacement material, several parameters affecting the mechanical properties of IBFC-cement composite have not been thoroughly investigated yet. Thus, this work aims to investigate the impact of IBFC as a cement replacement and the addition of the calcifying bacterium Lysinibacillus sp. WH on the mechanical and self-healing properties of IBFC cement pastes. The properties of the IBFC-cement pastes were assessed by determining compressive strength, permeable void, water absorption, cement hydration product, and self-healing property. Increases in IBFC replacement reduced the durability of the cement pastes. The addition of the strain WH to IBFC cement pastes, resulting in biocement, increased the strength of the IBFC-cement composite. A 20% IBFC cement-replacement was determined to be the ideal ratio for producing biocement in this study, with a lower void percentage and water absorption value. Adding strain WH decreases pore sizes, densifies the matrix in ≤ 20% IBFC biocement, and enhances the formation of calcium silicate hydrate (C-S-H) and AFm ettringite phases. Biogenic CaCO3 and C-S-H significantly increase IBFC composite strength, especially at ≤ 20% IBFC replacement. Moreover, IBFC-cement composites with strain WH exhibit self-healing properties, with bacteria precipitating CaCO3 crystals to bridge cracks within two weeks. Overall, this work provides an approach to produce a "green/sustainable" cement using biologically enabled self-healing characteristics.

Investigating the effects of superplasticizer and recycled plastics on the compressive strength of cementitious composites using neural networks

The potential application of neural network (NN) models to estimate the compressive strength (C S ) of cementitious composites under a variety of experimental settings and cement mixes was investigated. The data were extensively collected from previous literature, and the bootstrap resampling tests were applied to estimate the statistics of the parameter correlations. We find that the NN model that involves the coarse and fine natural aggregates (C A and F A ), superplasticizer (S P ) and recycled plastics (R P ) as the features can accurately predict the C S (R2 ∼ 0.9), without the need to specify the type of S P and the structure of R P in advance. The developed NN model holds promise for revealing the global dependency of C S on these parameters. It suggested that increasing 100 kg/m3 of C A could increase C S by ∼4 MPa, but the usage of C A more than 700 kg/m3 could negatively affect C S . How the C S varying with F A is apparently nonlinear. Within the optimum limit, adding 1 kg/m3 of S P could enhance the C S by ∼2 MPa. Contrarily, additional 1 kg/m3 of R P results in a decrease of ∼0.2 MPa of C S . The mixture-type independent models developed here would broaden our understanding of the global influential-sensitivity among these variables and help save cost and time in the industrial applications.

Properties of high-calcium and low-calcium fly ash combination geopolymer mortar containing recycled aggregate

This study presents the properties of a recycled aggregate geopolymer mortar made with a blend of high-calcium fly ash (HCF) and low-calcium fly ash (LCF). An experimental study was divided into two series. In series I, an effort was made to produce a more durable HCF geopolymer by partially replacing a portion of the HCF with LCF. A mortar with a 50:50 weight blend of HCF and LCF provided a high early strength and showed excellent potential in an acidic environment. In series II, recycled aggregate was used in the LCF-blended HCF geopolymer mortar. The results showed that the compressive strength of the geopolymer mortar decreased with an increase in the recycled aggregate content. The results also indicated that application of the mortar made with recycled aggregate under aggressive conditions should be avoided. However, a mixture with 25% recycled aggregate showed a compressive strength similar to that of the control mixture containing 100% natural aggregate.