A requirement for achieving sustainable concrete structures is to develop a quantitative method for designing concrete mixtures that yields the target rheological properties and compressive strength. Toward this objective, this paper proposes a mathematical model approach to improve the sustainability of the concrete industry. A postulation that packing density, a function of the concrete mixture, provides the link between concrete mixture, rheological properties, and compressive strength was investigated. Rheological models for yield stress and plastic viscosity, and a compressive strength model were adopted with packing density as a central variable. The rheological models employ a cell description that is representative of fresh concrete. The compressive strength model is based on excess paste theory to account for the concrete mixture proportions, gradation of aggregate particles, and porosity. An experimental program was developed to calibrate and test these models. Results revealed that packing density provides a consistent and reliable link, and that the concrete mixture composition can be designed to achieve the target rheological properties and hardened properties and ensure quality control. Consequently, a new mixture proportioning methodology was developed and proposed as an improvement to the ACI 211.1 mixture design method. Furthermore, a case study was conducted to test for the applicability and adequacy of this proposed method. This research outcome, which provides a quantitative approach to design concrete mixtures to meet specific strength requirements and rheology, can also be used to ensure quality control before concrete is cast.

In this paper, the applicability of the modified Andreasen and Andersen (A&A) particle packing model for designing pumpable flowing concretes, according to ACI 211.9R-18, is analyzed. An experimental investigation is undertaken to evaluate consistency, compressive strength, and shrinkage of flowing concretes designed with this model. The results show that the modified A&A model optimizes the particle size distribution of concrete ingredients and produces pumpable concretes according to ACI 211.9R-18. The distribution modulus of the model controls the combined grading, the ratio of coarse-to-fine aggregate, and the percentage of fine aggregate passing 300 and 150 μm. At a distribution modulus of 0.35, the model serves as the ACI’s recommended boundary limit for ideal-for-pumping combined grading. A high distribution modulus results in a high coarse-to-fine aggregate ratio and lowers the drying shrinkage of concrete. This insight enables a straightforward mixture design methodology that results in concrete that meets ACI 211.9R-18 recommendations.

This study aims to quantitatively analyze the fractal and multifractal characteristics of concrete at elevated temperatures. Based on the fractal geometry theory, fractal dimensions and multi-fractal spectrum are used to characterize the fractal propagation rules of defects in concrete. The results show that the fractal dimension D (box-counting method), can quantitatively describe the overall defect propagation inside concrete materials. Thus, the more diverse the defects, the larger this fractal dimension. Moreover, the fractal dimension, D’ (island method), does not exhibit considerable variations with different concrete loading types and temperatures. In addition, the multifractal spectrum can reflect the defect characteristics at different levels (local and global) while varying with the defect configurations. The capacity dimension, D0 (f(α)max), the entropy dimension, D1, the holder exponent of order zero, α0, and the signs and values of L–R may reflect the range distribution, size distribution, the degree of mass concentration, and the heterogeneity of defects within concrete, respectively. Moreover, the relationship between the fractal dimension, D, and the thermal damage can be expressed by a quadratic function whose correlation coefficient exceeds 0.99897. Therefore, the thermal damage in concrete at elevated temperatures can be quantitatively described by the quadratic function using the fractal dimension, D. This study provides theoretical and experimental bases for the fractal and, multifractal characteristics and the thermal damage evolution of concrete at elevated temperatures.

An experimental study was conducted to investigate the effect of using crumb rubber (CR) on improving the impact resistance and acoustic insulation of self-consolidating concrete mixtures. The study particularly aimed to maximize the percentage of CR in self-consolidating rubberized concrete (SCRC) to develop mixtures with high potential use in applications involving high-impact resistance, energy dissipation, and acoustic absorption. Several parameters were investigated—namely, percentage of CR (0 to 50% by volume of sand), type of supplementary cementitious materials (SCMs) (fly ash, slag, and metakaolin), binder content (500 to 550 kg/m3 [31.215 to 34.335 lb/ft3]), coarse aggregate size (10 to 20 mm [0.39 to 0.79 in.]), and entrained air. Tests included fresh properties, compressive strength, impact loading (drop weight on cylindrical specimens and flexural impact loading on small scale beams), ultrasonic pulse velocity, and acoustic emission measurements. The results indicated that it is possible to develop SCRC mixtures with optimum percentages of CR, which give promising results for concrete having higher energy absorption, acoustic insulation, and reduced self-weight compared to conventional concrete. The impact energy required to initiate the first visible crack and/or ultimate failure crack of the tested cylindrical specimens increased up to a CR replacement of 30%, while the impact energy required to break the tested beams increased up to a CR replacement of 20%. On the other hand, the acoustic absorption capacity of the tested mixtures continued to increase as the CR increased.

The water-cement ratio (w/c) is one of the most important parameters determining the quality of cement-based materials. Currently, there is no practical way to accurately determine this ratio after all the ingredients of concrete have been mixed, posing a significant quality-control problem for the construction industry. A new method has been developed to address this challenge whereby an electrical resistivity probe is immersed in fresh concrete, providing an instantaneous and accurate measure of a concrete’s w/c. Experiments were conducted on eight concrete mixtures designed according to the ACI 211.1 procedure, with varying w/c (0.30, 0.40, 0.50, and 0.60) and fly ash percentages (0 and 25%). The results demonstrate a strong direct correlation between the resistivity of fresh concrete and the w/c. Average w/c estimates based on measurements using the resistivity probe were within ±0.01 of the actual values for all mixtures tested.