In this review, we discuss microbiological and molecular concepts of Microbially Induced Calcium Carbonate Precipitation (MICP) and their role in bioconcrete. MICP is a widespread biochemical process in soils, caves, freshwater, marine sediments, and hypersaline habitats. MICP is an outcome of metabolic interactions between diverse microbial communities with organic and/or inorganic compounds present in the environment. Some of the major metabolic processes involved in MICP at different levels are urea hydrolysis, denitrification, dissimilatory sulfate reduction, and photosynthesis. Currently, MICP directed by urea hydrolysis, denitrification, and dissimilatory sulfate reduction has been reported to aid in the development of bioconcrete and has demonstrated an improvement in the mechanical and durability properties of concrete. Bioconcrete is a promising sustainable technology which reduces negative environmental impact caused by CO₂ emissions from the construction sector, as well as in terms of economic benefits by way of promoting a self-healing process of concrete structures. Among the metabolic processes mentioned above, urea hydrolysis is the most applied in concrete repair mechanisms. MICP by urea hydrolysis is induced by a series of reactions driven by urease (Ur) and carbonic anhydrase (CA). Catalytic activity of these two enzymes depends on diverse parameters, which are currently being studied under laboratory conditions to better understand the biochemical mechanisms involved and their regulation in microorganisms. It is clearly evident that microbiological and molecular components are essential to improving the process and performance of bioconcrete.

This work shows the mathematical development for the minimum cost of ECF (elliptical combined footings) subjected to biaxial bending due to the two columns, assuming that the distribution of soil pressure below the footing is linear and that the footing rests on elastic soil. There are no similar contributions on the subject of this article, as it is an innovative contribution in terms of its form. This work is developed in two parts: first, determine the minimum area in contact with the soil below the footing, and then the minimum cost is obtained. The formulation of the development by integration is shown to determine the moments, unidirectional shears, and punching shears acting on the critical sections, according to the ACI (American Concrete Institute) design code, and then the flowchart algorithm is applied to determine the solution using Maple Software, which is the main contribution of this article. Some authors show studies on the combined footings of various shapes such as rectangular, trapezoidal, strap, corner or L, and T, but there are none for ECF. Two numerical studies are shown with different length: the first with free ends in the longitudinal direction and the second with ends limited in the longitudinal direction to estimate the minimum cost of ECF under biaxial bending. A third numerical study is shown, with different allowable bearing capacities of the ground and with free ends in the longitudinal direction. Also, a comparison is developed between ECF and RCF (rectangular combined footings). The model for the design of ECF shows a savings of 7.17% with limited ends and a savings of 1.67% with free ends for the minimum area, and for the minimum cost, it shows a savings of 23.95% with limited ends and a savings of 9.14% with free ends rather than RCF. Therefore, the proposed development will be of great help to structural engineers specializing in foundations, as it represents significant savings.

This article presents a complete cost-optimized design for rectangular isolated footings (RIFs) under biaxial bending with a partially compressed contact area (PCCA) and an eccentric column, i.e., part of the base is in contact with the soil (generating compression), and the other part is not in contact with the soil (generating neither compression nor tension), and the soil pressure behaves linearly. The proposed model is presented by integration to find the moments in the critical sections, the bending shears in the critical sections and the punching shear acting on the RIF, and these are compared with those that must be resisted according to the standards (ACI 318-19) Some articles show complete designs for RIFs with a fully compressed contact area (FCCA) and an eccentric column, and other articles show only the minimum area (A_min) for RIFs with a PCCA and an eccentric column. The main contributions of this article are as follows: (1) the A_min is determined from the loads and moments, assuming that the loads and moments it resists must be greater than or equal to those acting on the RIF; (2) the minimum cost (C_min) is determined. Three numerical studies are described to demonstrate the advantages of this study over other models. The results indicate that, according to the studies presented in this article, savings of up to 45.99% for A_min and 93.62% for C_min can be achieved using the model proposed in this article (MPA); this occurs when the pressure acting on the foundation does not reach the maximum available soil pressure (p_max). Therefore, this paper could be of great use to engineers dedicated to the construction of foundations.

This study shows an optimal model to estimate the minimum area in contact with the soil for an EIF (elliptical isolated footing), assuming that the partially compressed area, that is, part of the surface below the base in contact with the ground, is compressed, and the other part is not compressed (the pressure of the ground is linear). There are works that show the minimum area for an elliptical isolated footing, but the surface below the base in contact with the ground is fully compressed. The model is developed by integration to determine the equations of the axial load and the two moments (X and Y axes) for the two cases. Two numerical studies are presented: Study 1 considers that the axial load varies, and the moments are equal and remain constant; Study 2 considers that the axial load varies, and the moments are different and remain constant. Two comparisons are also made with the model proposed by other authors (fully compressed area) and the new model (partially compressed area): In the first study, it is assumed that axial load and moment about the X-axis remain constant and moment about the Y-axis is variable; in the second study, it is assumed that the two moments remain constant and the axial load is variable. The results show that significant savings of up to 59.30% can be achieved in the first study and up to 65.67% in the second study in the area of contact with the ground. Another comparison is made between rectangular isolated footings and EIFs; the results indicate that savings of up to 63.18% can be achieved using EIFs. Therefore, this article will be of great help to specialists in foundation engineering.