Effect of corrosion on the bond behavior of steel-reinforced, alkali-activated slag concrete

Alkali-activated slag concrete (ASC) is regarded as one of the most promising sustainable construction materials for replacing ordinary Portland cement concrete (OPC) due to its comparable strength and outstanding durability in challenging environments. In this study, the corrosion of steel bars embedded in ASC and OPC was studied by means of an electrically accelerated corrosion test of steel bars in concrete. Meanwhile, the bond performance of the corroded steel bars embedded in ASC was tested and compared with corresponding OPC groups. The results showed that ASC and OPC behaved differently in terms of bond deterioration. The high chemical resistance of ASC decreased the corrosion of steel bars and, thus, increased the residue bond strength and the bond stiffness. © 2023 by the authors

Bond Stress between Steel-Reinforced Bars and Fly Ash-Based Geopolymer Concrete

Geopolymer concrete has been regarded as one of the most important green construction materials, which has been restrained in engineering applications partially due to a lack of bond studies. The structural performance of the reinforced concrete components primarily relies on the sufficient bond between the concrete and the reinforcing bars. Before being utilized in any concrete structure, GPC must demonstrate that it possesses understandable bond behaviour with commercial steel reinforcements. This work presents an experimental investigation on the bond stress of steel bars in reinforced geopolymer concrete (GPC) structures. Standard beam-end pull-out tests were conducted on GPC specimens reinforced with 16 mm plain and ribbed bars that were equipped with electrical resistance strain gauges. The longitudinal variation in the bond stress in the GPC beams during the pull-out tests was calculated and plotted, as well as the stress in steel bars. The cracks on the bond area of the GPC were compared with those of the corresponding ordinary Portland cement concrete (OPC), as well as the steel stress and bond stress. The results showed that the relative slip between plain bar and geopolymer concrete varies from 30–450 microns from the loaded end to the free end when the bond stress decreased by 83%. The relative slip between ribbed bar and geopolymer concrete varies from 280–3,000 microns from the loaded end to the free end when the bond stress decreased by 57%. Generally, GPC is different from OPC in terms of bond stress distribution

Disposal of solid waste as building materials: A study on the mechanical and durability performance of concrete composed of gold tailings

The purpose of this study is to explore the possibility of gold tailings as an alternative to natural river sand for preparing concrete, to solve the problems of rapid increase in gold tailings and insufficient natural river sand stock. Additionally, gold tailings upgraded by centrifugal separation are compared with untreated gold tailings. The performances and modification mechanisms of gold tailings on the mechanical strength and durability performance of concrete were investigated. The results demonstrate that concrete composed of gold tailings exhibits commendable mechanical and durability properties, with the optimal replacement level of natural river sand being 30%. Replacing river sand with gold tailings enhances the compressive and split tensile strengths of concrete, reduces water absorption, and improves its resistance to freeze-thaw cycles and chloride ion permeability, primarily owing to the pozzolanic activity and filling effect of the gold tailings. The upgrading of gold tailings not only changed altered the particle size but also changed the active SiO2 and Al2O3 content, thus, further enhancing the mechanical and durability of concrete. The study establishes that utilizing gold tailings in construction can serve as a viable substitute for river sand, thereby mitigating potential environmental repercussions associated with gold tailings. The findings hold promise for diminishing the reliance on river sand, thereby markedly enhancing resource sustainability

Bond Performance of Steel Bar and Fly Ash-Based Geopolymer Concrete in Beam End Tests

This paper presents a comprehensive investigation of the bond characteristics of steel bar reinforced geopolymer concrete (GPC). The ASTM A944 beam end tests were conducted on GPC beams reinforced with plain or ribbed bars. The bond–slip curves and the bond strength of GPC beams were obtained. The relationship between the bond stress and relative slip in plain and ribbed bar reinforced GPC has been represented by empirical formulae. The bond testing results were compared with those of corresponding ordinary Portland cement concrete (OPC) using statistical hypothesis tests. The results of hypothesis testing showed that GPC was significantly superior to OPC in terms of bond capability with plain bars and bond stiffness with ribbed bars. The statistical analysis indicated that the bond–slip relations derived for OPC are inapplicable to GPC; thus, new bond–slip relations are suggested to estimate the development of bond stress and relative slip between GPC and steel bars

Investigation of water ingress into uncracked and cracked cement-based materials using electrical capacitance volume tomography

Moisture and other dissolved ions can easily enter cracked cement-based materials, leading to a series of degenerating processes. Electrical capacitance volume tomography (ECVT) is a powerful approach for detecting and visualizing the three-dimensional (3D) water distribution inside cement-based materials. In this paper, the water ingress in mortar and concrete was monitored and visualized in 3D by ECVT. The feasibility of ECVT was first verified by conducting a moisture transfer experiment inside uncracked mortars. Then, the water ingress process into cracked mortar and concrete was monitored and visualized using this technique, which further confirmed the ability to image 3D volumetric water content in materials with highly heterogeneous permittivity. In addition, the water distribution inside the cracked and uncracked mortars was simulated utilizing two finite element models. The simulated results agree well with the ECVT reconstructed results, supporting the applicability of ECVT to image 3D water transfer in uncracked and cracked cement-based materials

Effect of Nano-CaCO3 on the Mechanical Properties and Durability of Concrete Incorporating Fly Ash

Concrete mixtures consisting of nanomaterials and fly ash have been shown to be effective for improving the performance of concrete. This study investigates the combined effects of nano-CaCO3 and fly ash on the mechanical properties and durability of concrete; the mix proportion is optimized through orthogonal experiments. In the first phase, nine concrete mixtures were prepared with three water-to-binder ratios (0.4, 0.5, and 0.6), three fly ash contents (15%, 20%, and 25% replacement of the cement weight), and three nano-CaCO3 contents (1%, 2%, and 3% replacement of the cement weight). Based on the orthogonal analysis, the optimal concrete mix proportion was determined as a water-to-binder ratio of 0.4, 20% fly ash, and 1% nano-CaCO3. In the second phase, further investigations were carried out to examine the superiority of the optimal concrete and evaluate the synergistic effect of nano-CaCO3 and fly ash. The results showed that nano-CaCO3 contributed to increasing the compressive strength of fly ash concrete at the early ages, but its effect was quite limited at later ages. Furthermore, the scanning electron microscopy analysis revealed that the seeding effect, filling effect, and pozzolanic effect were the primary mechanisms for the improvement of concrete performance

Dynamic mechanical behavior and damage properties of SHCC under high strain rate loading

Dynamic mechanical behaviors of strain-hardening cementitious composites (SHCC), considering the influence of strain rates, were investigated using split Hopkinson pressure bar (SHPB). Full-field strain evolution and cracking behavior of SHCC under high strain rate loading were investigated using high-speed digital image correlation (DIC) technology. Additionally, the damage properties of SHCC induced by high strain rate loading were analyzed using X-CT images and SEM observation. The results show that dynamic peak stress, strain, energy absorption capacity and dynamic increase factor (DIF) of SHCC are increased with the increase of strain rate. Full-field strain evolution of SHCC during the SHPB test demonstrates that the expansion in the vertical is larger than compression in the lateral under high strain rate loading. According to the X-CT images, dynamic load with a relatively higher strain rate will induce more fine cracks, and the number of cracks inside the specimen is more than on the surface. Moreover, plastic deformation of PVA fibers occurs under high strain rate loading based on SEM observation

Improving the salt frost resistance of recycled aggregate concrete modified by air-entraining agents and nano-silica under sustained compressive loading

This paper systematically investigated the combined effects of sustained compressive loading and the salt frost resistance for recycled aggregate concrete (RAC) incorporating air-entraining agents (AEA) and nano silica (NS). The effects of different RCA replacement ratios, freeze-thaw cycles, AEA dosage and compressive stress level on the freeze-thaw damage properties including the apparent morphology, mass loss rate and relative dynamic elastic modulus (RDEM) were discussed. The microstructure evolution of RAC samples before and after freeze-thaw cycles were characterized and analyzed through the SEM observation, microhardness measurement and X-CT tests. The synergistic modification mechanism of NS and AEA on RAC under salt frost action were investigated, and the link between the macroscopic and microscopic properties of air-entrained NS-modified RAC was further explored. The results showed that the RAC mixed with a certain amount of AEA and NS dosages exhibited the stronger salt frost resistance compared to that of control group. The effect of AEA dosage and compressive stress level exhibited similar changing trends on the salt frost resistance of RAC. When adding a moderate amount of AEA and applying a certain sustained compressive loading, the RDEM loss of RAC was reduced so that the salt frost resistance was partly improved. Similarly, the moderate AEA dosages can reduce the deterioration at ITZs of RAC. The compound use of NS and AEA proved to be as an efficient method to strengthen the microstructure of RAC, further improving the frost resistance under the coupled actions of sustained compressive loading and chloride salt attack. This study provides a feasible approach to improve the salt frost resistance of RAC under the coupled actions of sustained compressive loading, which is expected to promote the application and extension of RAC in complex environmental regions