Silica fume (SF) is the most commonly mineral admixture used for the production of high-strength concrete (HSC) due to its chemical characteristics of pozzolanic reactivity and physical filling effect. The objective of the present work is to compare the SF content by the chemical analysis of the pozzolanic reaction and the physical behavior by particle packing techniques. The first step of the study was to analyze the SF content to consume the calcium hydroxide (CH) produced during the hydration of Portland cement (PC), based on stoichiometric calculations. Then, the SF content for maximum packing density was obtained using analytical particle packing models and experimental tests. The compressive strength of the pastes was also measured. The results showed that the theoretical SF content for consuming CH is 15.6%, replacing PC. According to the packing density analytical models, the ideal SF content is 15% of the total fine materials. However, the experimental results indicated the use of a smaller SF content (10%). This difference between theoretical and experimental results is probably due to the high specific surface of the SF, which results in important surface forces between the grains, particle agglomeration and difficulty in SF densification with water.

Cement is considered the basic component with the highest environmental impact in construction, in terms of CO₂ emissions. As for the aggregates, the process of comminution of rocks, in addition to artificial sand, generates stone powder that ends up being stored outdoors, generating environmental damages. Thus, the replacement of cement by stone powder appears as an attractive alternative towards the sustainable concretes. In this context, the objective of this paper is to determine the maximum packing density in Portland cement, silica fume and stone dust pastes, to determine the optimal cement substitution content for the stone powder. In addition, it is intended to verify the influence of excess water on the consistency of the mixtures produced. The substitution was done in contents equal to 0%, 7%, 14% and 21% by volume and, for each content, the packing density was determined analytically by CPM model and combinations were reproduced experimentally. Excess water was checked by the mini Kantro cone test. The results showed that the higher cement substitution content of the stone powder obtained the higher packing density, experimental and analytical, and the higher workability, allowing economic and environmental advantages. Analyzing each material, the stone powder resulted in the highest packing density and silica fume is the lowest one. Therefore, finer particles resulted in lower packaging densities, due to the greater specific surface area, which demands more water. The agglomeration resulted in more empty gaps between the grains. In addition, mixtures flowability increased with the increase of the stone powder content. As the excess water is responsible for mixture lubrication, a higher packing density for a given volume of water improves the flowability.

The partial replacement of clinker by complementary cementitious materials can significantly contribute to the reduction of carbon emissions in the production of concrete. Another alternative to reduce these emissions is to increase the efficiency of the concrete, achieving higher compressive strength with lower consumption of cement. Particle packing models are efficient tools to optimize the composition of the matrix and contribute to the production of more eco-efficient concretes. In this context, the objective of the present study is evaluating the production of concretes with partial replacement of cement by stone powder, optimized by Alfred’s particle packing model, seeking to reduce cement consumption and CO2 emissions per MPa of compressive strength. The replacement content of cement by stone powder was 20% by mass (equivalent to 22.4% by volume). Concretes were produced with different distribution factor (q) - 0.37; 0.21; 0.45 - to verify the influence of fines on the flow between particles and on the efficiency of the produced concrete. The analyses were carried out in terms of properties in the fresh state, hardened state, and sustainability parameters (cement consumptions and CO2 emissions). The application of the proposed method resulted in a higher compressive strength than the expected for the water/cement ratio used (0.5). The most efficient concrete reached the compressive strength of 68 MPa with 240 kg/m3 of cement, which represents 3.5 kg of cement/m3/MPa and 3.1 kg of CO2/m3/MPa, a value below the references found in the literature for conventional concretes. Therefore, the proposed method allows to produce more eco-efficient concrete, contributing to the use of waste and reducing CO2 emissions.

The clinker production process, encompassing the extraction of its constituent minerals, the combustion of fossil fuels, and the calcining of limestone rocks, contributes to approximately 5 to 7% of global CO₂ emissions [¹ 1 V. Shobeiri, B. Bennett, T. Xie, and P. Visintin, "A comprehensive assessment of the global warming potential of geopolymer concrete," J. Clean. Prod., vol. 297, pp. 126669, 2021, http://doi.org/10.1016/j.jclepro.2021.126669. http://doi.org/10.1016/j.jclepro.2021.12... ]. In Brazil, this figure is notably lower at 2.6%, a result of high levels of additions allowed by standards [² 2 Sindicato Nacional da Indústria da Construção. Roadmap Tecnológico do Cimento Brasil, Rio de Janeiro: SNIC, 2019. ]. Therefore, several alternatives are being explored to mitigate the concrete environmental impact, including enhancing the efficiency of the cement industry, implementing carbon capture technologies, and increasing the use of additions in cement [² 2 Sindicato Nacional da Indústria da Construção. Roadmap Tecnológico do Cimento Brasil, Rio de Janeiro: SNIC, 2019. ]. For concrete producers and primary consumers of cement, a key strategy within their control is the rationalization of binder use through the adoption of more efficient mix design methods.

The use of supplementary cementitious materials (SCM) is a key to reducing CO2 emissions in the cement industry. This study analyzed concrete dosed with Alfred’s packing model, incorporating waste powders (mixed powder, concrete powder, brick powder, and glass powder) as SCM at replacement levels of 48%, 33%, 42%, and 32%, respectively. Properties such as absorption, voids index, compressive strength, dynamic modulus of elasticity, electrical resistivity, and environmental indexes were evaluated at 28 days. Results showed that brick powder exhibits pozzolanic activity, while the other powders act as fillers. Except for mixed powder concrete, all achieved high-strength concrete status (>50 MPa). All mixtures had negligible corrosion risk and binder and carbon indexes reduced by up to 37% and 35%, respectively. The study highlights the potential of recycled powders to lower emissions and promote circular economy practices.

Particle packing methods have been increasingly adopted to produce high-performance concretes (HPCs) with reduced porosity and enhanced durability. However, the mechanisms governing external sulfate attack (ESA) in densely packed systems remain insufficiently understood, particularly regarding the relative influence of pore structure and mechanical resistance on degradation processes. The relationship between microstructural parameters and the response of particle-packed HPCs subjected to sodium sulfate exposure (10% by mass) was investigated in this study. Concretes incorporating limestone filler and silica fume, and produced with limestone or granite aggregates, were evaluated through assessments of mass variation, dimensional variation, electrical resistivity and ultrasonic pulse velocity. The experimental results were interpreted using multiple linear regression to quantify the contribution of intrinsic material parameters to ESA-induced damage. Among the investigated variables, total porosity stood out, indicating that sulfate-induced deterioration in densely packed systems is predominantly controlled by pore network characteristics. Tensile strength also showed consistent relevance, suggesting its role in counteracting internal stresses generated by expansive reaction products. In addition, the mass variation test was considered the most suitable for evaluating ESA. The findings provide a microstructure-based framework for interpreting ESA in low-porosity cementitious materials and contribute to a more fundamental understanding of durability assessment of HPCs.