This paper presents the results of research on the properties of CEM II/A-F cements containing fine fraction of material from concrete rubble processing plant, as one of the main constituents of cement. The material obtained from concrete recycling plant was ground to produce a constituent that, according to EN 197-6, can be classified as constituent F. A portion of this material was further thermally processed by calcination at three different temperatures: 400 °C, 600 °C and 700 °C. The tests demonstrated a positive influence of thermal treatment on the properties of the binders, despite the relatively low content of hardened cement paste in the recycled material. A particularly beneficial effect, relative to the reference cement containing siliceous fly ash, when constituent F calcined at 600 °C was found.

Salt-freezing coupling is one of the main factors affecting the durability of recycled concrete. Investigating the chloride ion transport performance in recycled concrete containing recycled aggregate is essential to clarify the resistance of recycled concrete to chloride ion erosion due to the use of recycled aggregate produced from waste concrete. The objective of this paper is to investigate the migration behaviors and binding characteristics of chloride ions in recycled concrete, which were exposed to the salt-freezing coupling environment. The microstructure of the recycled concrete was conducted through scanning electron microscope (SEM), while the process of chloride ions migration was simulated by COMSOL software. The results indicated that the degree of recycled concrete, prepared by recycled coarse aggregate [RCA]and different particle size fly ash [NF], frost damage was higher in a 3 % NaCl solution compared to water. The contents of free chloride ions in recycled concrete subjected to freezing-thawing [F-T] cycle in water was minimally influenced by the NF content or the replacement rate of RCA. Under F-T conditions in a 3 % NaCl solution, increasing the NF content at the same replacement rate of RCA results in a decreasing-then-increasing trend in both the free chloride ion content and the chloride ion binding capacity in the concrete. Recycled concrete containing 15 % NF had a superior salt frost resistance compared to recycled concrete without NF or with ultrafine fly ash [SF]. With the replacement rates of RCA increasing, the contents of free chloride ions rose, the salt resistance of recycled concrete decreased. Using Fick’s second law, the chloride ion diffusion coefficient was calculated using MATLAB, and COMSOL software simulation accurately portrayed the diffusion state of free chloride ions in the recycled concrete.

The utilization of concrete in construction has seen a rapid increase due to its widespread use. However, the cement industry’s significant contribution to CO2 emissions and cli-mate change has prompted the exploration of alternative materials. Geopolymer concrete has emerged as a promising substitute to Portland cement in the construction industry in the wake of sustainability. In this study, the advantage of incorporating PVA fibers in geopolymer composites in optimum proportions to improve the overall mechanical proper-ties resulting in ductile concrete is being investigated. By systematically varying the PVA fiber dosage from 0 % to 1.5 % in increments of 0.5 %, along with different molarities ranging from 8 to 12 in two Mixes 1:1 and 1:3, several key properties, including compressive strength, tensile strength, flexural strength, and load-deflection curve were evaluated. The experimental results indicated that the addition of fibers had a negligible im-pact on compressive strength. However, a significant improvement was observed in flexural strength, energy absorption and ductility factor. Subsequently, a mix design model for geopolymer composites was developed, considering the influence of PVA fiber dos-age and molarities. The model was validated using a statistical technique called Response Surface Methodology [RSM], ensuring its accuracy and reliability. Overall, the study provides valuable insights into optimizing the dosage of PVA fibers in geopolymer composites, enabling production of sustainable and reinforced bendable concrete.

The performance of concrete / mortar is specially related to their composition and water to cement ratio. The use of Ordinary Portland cement [OPC] as binder increases the hydration heat and cost of cement and CO2 emissions. So the use of composite binder by reducing the amount of OPC and introducing mineral additions can be a useful solution. In this study, OPC was partially substituted with marble powder [MP] at various percentages (5, 10, 15 and 20%) and the effect of MP on the durability of self compacting mortars [SCM] exposed to chemical aggressions was investigated. Two aggressive solutions were used sodium sulfate [Na2SO4] and hydrochloric acid [HCl]. The dosages of the solutions were 5 and 1%, respectively. The results revealed that the use of marble powder is beneficial for improving the resistance of SCM to aggressive solutions. Adding 20% MP increased the resistance against sodium sulfate attack by 46% at 180 days. Using MP with content ranged between 10 to 20% was found to reduce mass loss by 1 to 0.47%.

In the existing practice, CO2, is mainly added to concrete through accelerated carbonation, which has many limitations, such as a low diffusion rate and the requirement of a large airtight chamber, which applies to pre-cast elements only. To overcome these limitations, this paper presents a novel beneficial use of CO2 in concrete production through the mineralization of CO2. CO2 is sequestered into a slurry of calcium-rich cementitious material in the first step of this process and then blended with the remaining materials to make concrete in the second step. The two-step mineralization process in the present work simplifies the CO2 mineralization into concrete and reaches 99% efficiency of applied CO2. The CO2 reacts with calcium-rich cementitious materials to form nano-scale calcium carbonate beneficially impacted concrete hydration. Microstructural analysis suggests that the carbonates seed the hydration and contribute to developing a stronger microstructure. For these reasons, the carbonation resistance of hardened concrete and the compressive strength is improved. The finding of the experimental investigation of the present research shows that an optimum amount of CO2 mineralization into concrete improves compressive strength by 18.2%, 18.8%, and 17.9% less carbonation at 180 days of testing. Furthermore, the major greenhouse gas, CO2, can be utilized, contributing towards sustainable and environmentally friendly production of concrete and construction practices.

The surface zone of the recycled aggregate plays a significant role in the strength and durability of concrete. In this research, various concrete series incorporating natural coarse aggregate [NCA], untreated recycled coarse aggregate RCA(UN), mechanical scrubbing treated coarse aggregate RCA(MS), sulfuric acid treated coarse aggregate RCA(H2SO4) and hydrochloric acid treated aggregate RCA(HCl) were investigated. Manufactured sand was used as an alternative to natural river sand in five series of concrete with 100% replacement ratio. The mechanical properties: compressive, split tensile, and flexural strength, respectively, were determined at the age of 28 and 56 days. Durability properties: water absorption, drying, sulfuric acid, sodium sulphate and sorptivity test were determined at the age of 28, 56 and 90 days and the results were compared to reference concrete. According to the results, RCA(UN) was found to marginally decreased the concrete performance, and the above mentioned treated aggregate shows a significant improvement in overall performance compared to RCA(UN), especially RCA(MS), which enhances the concrete more significantly than other methods. Moreover, the scanning electron microscope results also emphasize the enhanced microstructure of treated recycled aggregate in concrete. The photographic view of the cross sections of the samples shows a superior interfacial transition zone in all kinds of treated aggregate concrete than in untreated recycled aggregate concrete.

A review of concrete durability at several sections of the new built expressways in Poland is presented. Two-layers jointed plain concrete pavements were constructed using a slip-form technology. For freeze-thaw and deicing salts durability of concrete the specified air void properties, including the spacing factor and the microvoids content, was evaluated on core specimens drilled from the constructed pavements. The observed system of fine air voids indicates optimal features for increased frost and scaling resistance without a significant negative impact on strength. The correlation was established between the microvoid content in the hardened concrete and the data of the Super Air Metre on fresh concrete mix was established. Concrete durability in high moisture environment, combined with fatigue traffic load and external supply of alkaline deicing salt solutions, was considered using newly developed principles of nonreactive aggregate selection. The aggregate selection based on petrographic analysis and the assessment of expansive behaviour of concrete was fully confirmed using the performance tests with external supply of sodium chloride. The suitability of the established methodology for durability acceptance testing for exploration of alternative materials for paving is discussed.

Valorization of agricultural wastes is important both economically and environmentally. This study aimed to investigate the use of biochar as a filler to improve the mechanical properties of mortar and to help sequestrate CO2. The biochar was produced by pyrolysis of apricot kernel shell at 500 °C. Nanobiochar particles with dimensions less than 500 nm were obtained by high-energy ball milling process. Scanning electron microscope was used for determining the morphology of nanobiochar. The nanobiochar at different volume percentages [0.00-0.04-0.06-0.08-0.12-0.15%] was added to mortar. The mortar was casted into 40x40x160 mm molds. After water curing at 20°C for 28 days, compressive strength and flexural strength tests were performed. The mixture containing 0.04% nanobiochar by volume had an increase in flexural and compressive strengths by 5% and 15% respectively, while its fracture energies for flexure and compression increased by 98% and 38% respectively compared to the reference mortar. Furthermore, the mixture having 0.12% volume had an increase in flexural and compressive strengths by 32% and 11%, respectively, while the increase in fracture energies for flexure and compression was 52% and 25%, respectively, compared to the reference mortar. The mechanisms of nanobiochar effect on flow, strength, and fracture energy were enlightened. The nanobiochars bridge the cracks, divert the cracks, act as hydration nucleation sites, enhance the matrix by its porous structure, and developed internal curing that led to increase in strength and fracture energy. This study suggests that the biochar produced from the apricot kernel shell has the potential to be used as a carbon sequestering mixture to improve performance of mortar and thereby utilizing waste as a construction material, contributing to the economy and environment.

An attempt was made to adjust the kind of organic additives to the components of the mass for the magnesia-chromite products. This was done using Sanderson’s concept of electronegativity and molar electronegativity. Four organic additives were selected and their influence on the properties of the refractories was studied by performing a total factorial experiment 24. The basic properties of the refractories are presented in the form of seven response functions, six of which are described by statistically verified equations. The most favourable options were selected on the basis of six criteria that characterise the materials. The introduction of organic additives as slip agents into the mass, resulted in an improvement in practically all properties of the magnesia-chromite materials after firing. The purposefulness of the additive composition was demonstrated.

Today, the increase in heating and energy costs has increased the importance of insulation in buildings and new searches are being made for this purpose. As a result of these searches, studies on the production of lightweight concrete have come to the forefront, to improve the insulation properties of concrete. In this study, the usability of hazelnut shells, one of the important agricultural products of Turkey, which are post-harvest waste materials as a lightweight aggregate in concrete, was investigated. To this end, concrete was produced by replacing the aggregate with hazelnut shell by 3%, 6%, 9%, 12% and 15%, and the physical, mechanical and thermal properties of this concrete, were examined. As a result of the study, it was determined that hazelnut shell, which is an agricultural waste, could be used as aggregate in the production of concrete and that lightweight concrete with sufficient strength and durability and improved heat and sound insulation could be produced, provided that the amount of hazelnut shell to be added to the mixture would not be more than 10% of the aggregate.