Search Results (53)

Concrete is used globally due to its useful mechanical and durability properties. However, concrete requires a massive amount of cement, which is the second-largest source of carbon emission (5–7% of global CO₂ emissions) due to its high energy consumption. The gelatinization effect of corn starch as a binder has been explored in the place of cement in concrete. However, there is a need to optimize the various processing conditions to enhance the material strength of the corn starch-based material known as CoRncrete. Two experiments were conducted to optimize the ratio of sand, starch, water, curing temperatures, and time. The compressive and tensile strength of the CoRncrete samples were analyzed. The results showed that the optimum processing conditions having a sand grain size of 0.250–0.425 mm, a mixture ratio of starch, water, and sand 1:1:5, and curing temperature and time of 110 °C and 24 h can yield a maximum compressive strength up to 18.9 MPa. Statistical analysis revealed that the size of sand grains and curing temperatures had the most significant impact on the material’s strength. Microstructural analysis, employing scanning electron microscopy (SEM) and micro-computed tomography (microCT), unveiled numerous internal pores and cracks within the hardened cubic blocks, which significantly decreased the strength. Consequently, future investigations should concentrate on reducing internal pore spaces and cracks to enhance the durability of CoRncrete. Full article

Currently, the cement sector has become aware of the economic and environmental advantages of replacing clinker with other supplementary cementitious materials that have a lower carbon footprint in the design of eco-cements. In this study, hydrotalcite, a natural as well as synthetic clay, which can be fabricated at the cement plant site, was used as such an addition. The objective of this work was to evaluate the behavior of its physical–mechanical properties and durability in pastes and mortars, using a magnesium-type commercial hydrotalcite, Mg₆Al₂(OH)₁₆CO₃·4H₂O, as a substitute material for 10, 20 and 30% by weight of ordinary Portland cement (OPC). The mechanical strength was not affected by the substitution, the resistance to chlorides increased, as the hydrotalcite (HT) was able to bind chlorides, and the resistance to carbonation increased at 3 months but was almost the same as the reference specimen at 6 months, which indicates the need to have longer test durations. Full article

This study examined the fracture and failed performance of foamed concrete materials by testing normalized notched beams under three-point bending via three methods: inverse analysis, digital image correlation (DIC), and finite element modeling (FEM). It also discussed both experimental and FEM characteristics. However, inverse analysis is only applicable for specimens with a notch height of 30 mm. Bilinear softening of the tested beams was estimated to identify the fracture energy (G_F), critical crack length (a_c), and elastic modulus (E). Additionally, the fracture toughness was calculated by adopting the double-K method (initiation fracture, unstable fracture, and cohesive fracture). Two-dimensional FEA modeling of the fracture was conducted using the traction-separation law (TSL), incorporating the extended finite element method (XFEM) and cohesive zone (CZM) techniques. A finite element sensitivity for the XFEM and CZM was performed, with the global mesh size of 2 and the damage stabilization cohesion of 1 × 10⁻⁵ showed good convergence and were used in other models. Further comparison of the DIC experiment findings with those from the FEM demonstrated good agreement in terms of crack propagation simulation. Full article

The emission of carbon dioxide gas from the cement manufacturing industry has raised concerns about global warming. Geopolymer concrete (GC) is gaining attention as a sustainable and environmentally friendly alternative to traditional cement concrete. The current study focused on using local clay to synthesize and characterize metakaolin-based GC with varying percentages of nanosilica (NS) (1.5%, 3.0%, 4.5%, 6.0%, and 7.5% by weight of MK content) using NaOH/sodium silicate. The geopolymer specimens were cured at room temperature for 28 days, and their workability, compressive, tensile, and flexural strengths were measured to evaluate the influence of NS on the concrete’s mechanical properties. The study found that the compressive, tensile, and flexural strengths of the GC increased gradually up to 6.0% NS, but any further increase in its ratio resulted in a reduction in mechanical characteristics. The study concludes that the addition of 6.0% NS in metakaolin (MK)-based GC produces the highest mechanical properties, improving the compressive strength of the GC mix by 34.3% compared to the control GC mix and improving the flexural and split tensile strengths by 39% and 37%, respectively, compared to control GC strengths. Furthermore, the statistical analysis confirms nano-silica’s significant impact on geopolymer concrete’s mechanical properties, emphasizing its role in improving performance and sustainability as an alternative to cement-based materials. Full article

Environmental pollution is one of the most serious and global problems for humans. Photocatalysis is a promising technology to control environmental pollution via the utilization of semiconductor materials as a photocatalyst. In this study, iron-doped TiO₂ nanotubes (Fe/TiNTs) with an increased photocatalytic effect at longer wavelengths compared to undoped TiNTs were used, and the effect on the early hydration and mechanical properties of the main clinker phase tricalcium silicate (C₃S) was investigated for the first time. Prior to the incorporation of nanotubes into C₃S, it was treated with a supersaturated Ca(OH)₂ solution. The addition of 1 and 2 wt.% of Fe/TiNTs into the C₃S system significantly accelerated the course of hydration. The degree of hydration for the hydration products after 8 h, 1 d and 7 d have improved. The enhancement of compressive strength after 7 d, 14 d and 28 d were observed compared to normal TiO₂ nanotubes (TiNTs). Treating Fe/TiNTs with a supersaturated Ca(OH)₂ solution revealed a stronger interaction between Ca²⁺-ions and nanotubes. Fe/TNTs were synthesized via a modified hydrothermal process. The study shows that Fe/TiNTs can be used as a nanomaterial in cement-based building materials due to their enhanced interaction with the system. Full article

Early-age cracking during the plastic stage is unsightly and a cause of future durability problems. This paper investigates the effects of various simple curing methods used in practice to enhance early-age concrete cracking performance, including covering concrete with a plastic sheet and wet hessian fabric, surface power floating and use of cold water in the mix. The benefits offered by the use of three standard curing admixtures (Safecure Super concrete, Safecure Super 90W-10%, and superplasticizer), as well as recycled tire steel fibres at 40 kg/m³, are also examined. A digital image processing (DIP) technique is used to measure the crack widths, whilst the temperature in the concrete is measured via a thermocouple. The results show that all the concrete curing methods are successful in restraining micro and plastic shrinkage cracks, although the use of recycled tire steel fibre (RTSFC40) is most effective in eliminating micro and plastic shrinkage surface cracks. All of the examined methods are compared in terms of the speed and cost of application, quality of the surface finish and environmental credentials. This study will inform best practice on enhancing the durability and sustainability of concrete structures, particularly for slab-on-grade applications. Full article

Alkali–silica reactivity (ASR) is one of multiple reactions responsible for premature loss in concrete infrastructure service life. ASR results in the formation of expansive, white-colored gel-like material which results in internal stresses within hardened concrete. ASR-induced stresses result in concrete cracking, spalling, and increased reinforcement steel corrosion rates. The main objective of this research is to improve the conditions of concrete infrastructure projects by mitigating ASR’s damaging effect. The expansion of accelerated mortar bars poured using fine aggregates collected from different sources is measured versus time to evaluate the aggregates’ reactivity. Different percentages of supplementary cementitious materials (SCMs), including class C fly ash and microsilica, were used in remixing mortar bars to evaluate the efficiency of different types of SCMs in mitigating mortar bar expansion. The research findings showed that SCMs can mitigate ASR, thus decreasing mortar bar expansion. The efficiency of SCMs in ASR mitigation is highly dependent on the incorporated SCM percentage and particle fineness. Silica fume, having the smallest particle size, displayed higher rates of ASR mitigation, followed by fly ash. The outcomes of this research will assist design engineers in avoiding future losses due to ASR cracking in concrete infrastructure projects, and reduce the excessive need for maintenance, repair, and replacement activities. Full article

Additive manufacturing is becoming increasingly important in the construction industry. Wire arc additive manufacturing (WAAM) can be integrated into the selective paste intrusion (SPI) to enable the simultaneous printing of reinforced concrete. The bond behavior of a WAAM reinforcement was investigated with pull-out tests and compared to alternative reinforcement types to analyze the stress transfer between the different components. In the first step, the surface of all the reinforcement types was recorded using a laser-based line scan measuring system. This permits the evaluation of the surface parameters, such as the surface roughness R_q, or the related rib area f_R. The WAAM reinforcement showed a bond behavior in the pull-out tests that was comparable to a reinforcing steel bar. Both the bond stresses achieved, and the occurring scatter of the measurement results at the characteristic slip values were almost the same. Even without existing transverse ribs, the WAAM reinforcement reached maximum bond stresses similar to the reinforcing steel. An evaluation of the surface roughness revealed a linear relationship with the maximum bond stress achieved with a logarithmic scaling of R_q. The bond work W_τ, which is a measure of the system stiffness, showed that WAAM reinforcements and reinforcing steel bars have approximately similar behavior. Full article

Analysis of the use of reinforced concrete structures confirmed the destruction of reinforced products based on Portland cement due to stray currents, which makes it impossible to achieve the required durability and reliability of structures. The present work shows the results of a study on the diffusion permeability of samples with different degrees of electrical conductivity. The relative value of the electrode potential was measured by the open circuit potential method. The novelty of this work is its analysis of the quantitative and qualitative characteristics of the structure of the mineral matrix with specified electrical properties after long-term exposure to electrochemical corrosion. In this work, an assessment was carried out, for the first time, on the effects of electrochemical corrosion on modified composites with predominantly electrically conductive and electrically insulating properties. An increase in the electrical conductivity of the composite was found to reduce the potential difference. The use of such composites helped protect the reinforcement from electrochemical corrosion. Full article

Dehydration of concrete floor slabs is a critical step to ensure that the flooring material adheres properly and that there is no moisture-related damage to the floor after installation. Dehydration in a cold climate is often a slow process, which can have a big impact on the overall duration of the construction project, and corresponding measures are often taken to accelerate the drying process, especially in constructions exposed to a cold climate. One common method, typically used to accelerate dehydration in cold weather, is to introduce internal heating cables into the slab. This method reduces the dehydration time, but may not be the best solution from a sustainability perspective. This paper presents a concept study of concrete flooring in a cold climate from a cradle to practical completion perspective. The study focused on the environmental and material aspects of the dehydration of concrete floors in a cast-in-place house. This paper showed that concretes with high water-cement ratios, which are typically preferred due to their low CO₂ emissions, may require measures for accelerated dehydration, which ultimately results in a higher environmental impact. The importance of environmental studies is also highlighted to fully understand the environmental aspects of construction. Full article

The bleeding of cementitious materials corresponds to the settlement of the granular skeleton accompanied by the accumulation of water at the surface (bleed water). Part of this water (internal bleeding) remains trapped under the aggregates (sand or gravel) or the reinforcements. The excess of this trapped water can weaken the bond between the cementitious matrix and the aggregates (or the reinforcements), which affects the mechanical performance and durability of the material. This study aims to investigate the effect of excessive bleeding induced by superplasticizer on the properties of mortars. For this, a study of cement paste bleeding in the presence of superplasticizer was carried out. The effects of the water-to-cement ratio (w/c) and the superplasticizer (SP) dosage on this bleeding have been characterized. Then, the influence of the proportion of sand on the bleeding was examined by varying the sand/cement (s/c) ratio. The water trapped by sand (internal bleeding) was determined by the difference between the external bleeding on the cement paste and the external bleeding on the corresponding mortar. The results show that the internal bleeding increases with the s/c ratio and the SP dosage, until it reaches a plateau. The effect of the internal bleeding on the mechanical properties and the porosity of the mortar were then examined. Microscopic observations were made to assess the quality of the paste/sand bond. The results showed that the internal bleeding causes a degradation of the paste/sand bond (a more porous bond), resulting in a decrease in the mechanical strength (by 30% for compressive strength and 25% for flexural strength) of the hardened mortar. Full article

Earthen construction is one of the world’s oldest and most popular construction methods, and it is still the target of prejudice due to the loss of ancestral knowledge. Due to the need for more effective and healthy building solutions, this study conducted a survey to determine the interest and knowledge of construction professionals regarding sustainable and natural materials and building techniques to understand how open these professionals are to changes in their working methods and if they identify urgency in that change. With the intent of proving the durability of earthen construction materials, laboratory research was developed which involved the preparation and performance evaluation of samples of earthen elements from the most-used techniques: rammed earth and compressed earth blocks. This evaluation was performed using the accelerated erosion test, simulating periods of rainfall and drying, and the post-test loss of resistance was also evaluated. According to the results obtained from the research survey, there is a predominant lack of knowledge about earthen construction and other traditional and sustainable materials. On the other hand, the experiments demonstrated that earthen construction can be durable when using either a small percentage of stabilizing material or a covering plaster. Full article

According to pavement design principles, the subgrade or soil layer serving as the foundation for pavement depends on the properties and stiffness of the soil material. The resilient modulus (M_R) is the absolute measure of the bearing capacity of the subgrade for pavement design. However, due to the complexity of M_R testing, indirect methods are chosen to determine M_R. In this context, the CBR test is considered a practical tool for determining the strength of the subgrade, but the use of the correlations of M_R-CBR has caused great controversy in the scientific community. Nevertheless, such correlations are widely used in practice for pavement design, and the question of their influence on design results is always raised. Therefore, the present study investigates the use and applicability of the M_R-CBR correlations for the subgrade with respect to the design of flexible pavements, with the aim of optimizing the thickness and bearing capacity of the unbound base/sub-base. Based on the previous debate on the use of M_R-CBR correlations, this study first investigates the main correlations between M_R and the CBR index based on a thorough review of the literature. Using the properties of certain medium-grained soils used in practice and the corresponding values of M_R, estimated by the various M_R-CBR correlations reported in the international literature, a theoretical pavement design is then carried out on the basis of a sensitivity analysis. A major outcome of the sensitivity analysis is the identification of the most optimal correlation for estimating M_R in pavement design, while the development of a global M_R-CBR correlation applicable to most types of soil materials used in pavement construction remains an important topic for future research. Full article

This study aimed at evaluating the effect of blended binders on the stabilization of clayey soils intended for use as road and pavement materials in selected regions of Sweden. The stabilization potential of blended binders containing five stabilizers (cement, bio fly ash, energy fly ash, slag and lime) was investigated using laboratory tests and statistical analysis. Soil samples were compacted using Swedish Standards on UCS. The specimens were stabilized with blended mixtures containing various ratios of five binders. The effects of changed ratio of binders on soil strength was analyzed using velocities of seismic P-waves penetrating the tested soil samples on the day 14 of the experiment. The difference in the soil surface response indicated variations in strength in the evaluated specimens. We tested combination of blended binders to improve the stabilization of clayey soil. The mix of slag/lime or slag/cement accelerated soil hardening process and gave durable soil product. We noted that pure lime (burnt or quenched) is best suited for the fine-grained soils containing clay minerals. Slag used in this study had a very finely ground structure and had hydraulic properties (hardens under water) without activation. Therefore, slag has a too slow curing process for it to be practical to use in real projects on stabilization of roads. The best performance on soil stabilization was demonstrated by blended binders consisted of lime/fly ash/cement which considerably improved the geotechnical properties and workability of soil and increased its strength. We conclude that bearing capacities of soil intended for road construction can be significantly improved by stabilization using mixed binders, compared to pure binders (cement). Full article

The study examines the effects of modifying PG 64-22 asphalt binder with Crumb Rubber Modifier (CRM) and processed oil on its properties. The binder was tested at different temperatures, and different amounts of CRM and processed oil were added to the binder. The modified binders were also aged using different procedures. The study found that adding processed oil to CRM-modified binders reduces viscosity and improves workability, while CRM improves the rutting resistance. However, the addition of processed oil reduces the binder’s rutting performance. The study also found that CRM and processed oil improve the low temperature cracking resistance. The study’s results indicate that co-modifying CRM binders with processed oil resulted in a significant reduction in viscosity values, resulting in improved workability. The results also showed that increasing the processed oil concentration from 6% to 12% caused a viscosity reduction of 27%, 34%, 33%, and 31% for modified binders containing 0, 5%, 10%, and 15% CRM, respectively. Even though the addition of processed oil results in a reduction in the rutting performance of asphalt binder, the addition of CRM significantly improved the rutting resistance of asphalt binders. The CRM binder containing processed oil decreased the G*sin δ values, and the content of 6% processed oil containing 5%, 10%, and 15% CRM decreased by 28%, 17%, and 11%, respectively, while the 12% processed oil-modified asphalt binder showed a reduction in G*sin δ by 5%, 13%, and 22%, respectively. The BBR results for modified asphalt binders showed that the incorporation of CRM and processed oil improved the low temperature cracking resistance significantly. The stiffness values with 6% processed oil containing 5%, 10%, and 15% CRM were observed to be 118, 97, and 80 MPa, respectively, while at the same temperature for the same CRM contents with 12% processed oil, the stiffness values were found to be 89, 72, and 56 MPa, respectively. Full article