Search Results (406)

Rapid pavement repair demands materials that combine accelerated strength gains, dimensional stability, long-term durability, and sustainability. However, finding materials or formulations that offer these balances remains a critical challenge. This study systematically evaluates two polymer-modified belitic calcium sulfoaluminate (CSA) concretes—CSAP (powdered polymer) and CSA-LLP (liquid polymer admixture)—against a traditional Type III Portland cement (OPC) control under both laboratory and realistic outdoor conditions. Laboratory specimens were tested for fresh properties, early-age and later-age compressive, flexural, and splitting tensile strengths, as well as drying shrinkage according to ASTM standards. Outdoor 5 × 4 × 12-inch slabs mimicking typical jointed plain concrete panels (JPCPs), instrumented with vibrating wire strain gauges and thermocouples, recorded the strain and temperature at 5 min intervals over 16 weeks, with 24 h wet-burlap curing to replicate field practices. Laboratory findings show that CSA mixes exceeded 3200 psi of compressive strength at 4 h, but cold outdoor casting (~48 °F) delayed the early-age strength development. The CSA-LLP exhibited the lowest drying shrinkage (0.036% at 16 weeks), and outdoor CSA slabs captured the initial ettringite-driven expansion, resulting in a net expansion (+200 µε) rather than contraction. Approximately 80% of the total strain evolved within the first 48 h, driven by autogenous and plastic effects. CSA mixes generated lower peak internal temperatures and reduced thermal strain amplitudes compared to the OPC, improving dimensional stability and mitigating restraint-induced cracking. These results underscore the necessity of field validation for shrinkage compensation mechanisms and highlight the critical roles of the polymer type and curing protocol in optimizing CSA-based repairs for durable, low-carbon pavement rehabilitation. Full article

This study investigates the combined influence of superabsorbent polymers (SAPs) with distinct absorption kinetics and extended mixing sequences on the rheological, mechanical, and transport properties of high-performance concrete (HPC). Two SAPs—an ionic acrylamide-co-acrylic acid copolymer (SAP-P) and a non-ionic acrylamide polymer (SAP-B)—were incorporated at an internal curing level of 100%. The impact of extended mixing times (3, 5, and 7 min) following SAP addition was systematically evaluated. Results showed that longer mixing durations led to increased superplasticizer demand and higher plastic viscosity due to continued water absorption by SAPs. However, yield stress remained relatively stable owing to the dispersing effect of the added superplasticizer. Both SAPs significantly enhanced the static yield stress and improved fresh stability, as evidenced by reduced surface settlement. Despite the rheological changes, mechanical properties—including compressive and flexural strengths and modulus of elasticity—were consistently improved, regardless of mixing duration. SAP incorporation also led to notable reductions in autogenous and drying shrinkage, as well as enhanced electrical resistivity, indicating better durability performance. These findings suggest that a 3 min extended mixing time is sufficient for effective SAP dispersion without compromising performance. Full article

This study investigates the influence of superabsorbent polymer (SAP) particle size on the mechanical and shrinkage behavior of concrete. Five concrete mixtures were prepared using SAPs with varying size ranges: 150–300 µm, 300–600 µm, 600–1800 µm, and a blended mix combining 300–600 µm and 600–1180 µm. The primary focus was on evaluating compressive strength, elastic modulus, autogenous shrinkage, drying shrinkage, and total shrinkage. The mechanical performance and dimensional stability were measured at different curing ages, and microstructural analysis was conducted using X-ray fluorescence (XRF) at 7 days to examine changes in chemical composition. Results showed that smaller SAP sizes contributed to more homogeneous internal curing, improved hydration, and higher matrix density. In contrast, larger SAP particles were more effective in reducing shrinkage but slightly compromised strength and stiffness. This study emphasizes the importance of selecting appropriate SAP particle sizes to balance mechanical integrity and shrinkage control, contributing to the development of high-performance concrete with reduced cracking potential. Full article

Full-section interval casting technology was adopted for the integral immersed tube of the Chebei Immersed Tunnel. Field tests (Chebei Immersed Tunnel) were conducted to establish the time-dependent development of the concrete shrinkage strain of the full-section casting segments. And laboratory experiments were then carried out to investigate the influence of factors such as the reinforcement ratio and stress, expansive agent content and composition, fly ash content, and curing temperature and humidity on the expansive effect of calcium–magnesium composite expansive agents. Field tests revealed that casting segments exhibit initial expansion followed by shrinkage, reaching a final strain of 348 με (microstrain). Laboratory investigations demonstrated that reinforcement (20–30 MPa stress) in post-casting belts effectively restrains segments without compromising the performance of calcium–magnesium composite expansive agents. The optimal 5:3:2 ratio of CaO, MgO 90s, and MgO 200s agents controlled shrinkage strain within 80 με by combining CaO’s rapid early expansion with MgO’s sustained effect. Field validation confirmed the mix’s effectiveness in preventing cracking, with key findings: (1) fly ash content and curing conditions significantly influence expansive behavior, and (2) shrinkage development can be precisely regulated through agent composition adjustments. Full article

The paper deals with the issue of obtaining iron-sulfur-containing binders through their mechanochemical treatment using mutual neutralization and detoxification structure formation, and the curing stage of arbolite concrete composites based on industrial waste under long-term loading were also studied. Due to abrasion and impact, the mutual neutralization and detoxification methods of industrial waste toxic components through their mechanochemical treatment on the structures of ball mill LShM-750, were used to obtain iron-sulfur-containing binders. Pyrite cinders acted as oxidizing agents, and elementary technical sulfur had reduced properties. To determine the rate of creep strain growth, the load on prism samples was applied in the form of specially made spring units at stress levels of 0.15 R_bn, 0.44 R_bn, and 0.74 R_bn, where R_bn is the prism strength of iron-sulfur-containing arbolite concrete in compression. The strength and fracture formations of lightweight iron-sulfur concrete were studied using strain gauge apparatus and depth strain gauges glued on shredded reed fibers using adhesive, installed before concreting. It was revealed that the introduction of a sulfur additive within the range from 10 to 13% increases the compressive strength of iron-sulfur-containing concrete composites prepared with that of mortars at a water/solid ratio equal to 0.385 in wet and dry states. It is found that the deformations occurring under applied load growth proportionally to it, and deviation from this regularity was observed for lightweight iron-sulfur-containing concrete only at high compressive stresses. It was also proved that the destruction of iron-sulfur-containing arbolite occurs sequentially. First, the destruction of the mortar component is observed, and then the organic aggregate in the form of crushed reed fiber is destroyed. It was confirmed that arbolite concrete composite can be used as an effective wall material for civil engineering structure, especially in seismic regions of Kazakhstan. Full article

Although 3D-printed concrete (3DPC) offers advantages such as faster construction, reduced labour costs, and minimized material waste, concerns remain about its long-term durability. This review examines these challenges by assessing how the unique layer-by-layer manufacturing process of 3DPC influences key material properties and overall durability. The formation of interfacial porosity and anisotropic microstructures can compromise structural integrity over time, increasing susceptibility to environmental degradation. Increased porosity at layer interfaces and the presence of shrinkage-induced cracking, including both plastic and autogenous shrinkage, contribute to reduced durability. Studies on freeze–thaw performance indicate that 3DPC can achieve durability comparable to cast concrete when proper mix designs and air-entraining agents are used. Chemical resistance, particularly under sulfuric acid exposure, remains a challenge, but improvements have been observed with the inclusion of supplementary cementitious materials such as silica fume. In addition, tests for chloride ingress and carbonation reveal that permeability and resistance are highly sensitive to printing parameters, material composition, and curing conditions. Carbonation resistance, in particular, appears to be lower in 3DPC than in traditional concrete. This review highlights the need for further research and emphasizes that optimizing mix designs and printing processes is critical to improving the long-term performance of 3D-printed concrete structures. Full article

This study analyzed the effects of curing and maturation on the formation of shrinkage strain and destructive processes in concrete. Experimental tests were performed on commonly used concrete, class C30/37, with basalt aggregate and blast furnace cement tested: at constant temperature after water curing, at constant temperature without water curing, and under cyclically changing temperature without prior curing. Shrinkage strain was measured for 46 days with an extensometer on 150 × 150 × 600 mm specimens, and the acoustic emission (AE) method was used to monitor microcracks and processes in concrete in real time. The results were compared with the model according to EN 1992-1-1:2023. It was found that this model correctly estimates shrinkage strain for wet-curing concrete, but there are discrepancies for air-dried concrete, regardless of temperature and moisture conditions (constant/variable). Correlation coefficients between shrinkage strain increments and process increments in early-age concrete are proposed. Correlations between shrinkage strain and destructive processes occurring in concrete were confirmed. It was found that by using correlation coefficients, it is possible to estimate internal damage in relation to shrinkage strain. The results indicate the need to develop guidelines for estimating shrinkage strain in non-model environmental conditions and demonstrate the usefulness of the nondestructive AE method in diagnosing early damage, especially in concrete structures exposed to adverse service conditions. Full article

Three-dimensional printing is rapidly growing in applied dentistry. In order to print faster, increase workflow, and minimize the consumption of resin material, it is important to use the right printer and the correct printing orientation. The objective of the present report is to analyze the flexural strength of specimens realized with two different dental light-curing resins (Keyguide and C&B) obtained from two different Digital Light Processing (DLP) 3D printers. Different printing orientations (0°, 45°, and 90°) were evaluated. 3D Builder, MeshMixer, RayWare, and Chitubox software were used to design the resin specimens. A total of 15 Keyguide and 15 C&B specimens in the shape of a rectangular parallelepiped, with dimensions of 2 mm × 2 mm × 25 mm, were obtained with the Sprintray Moonray S 3D printer, and the 15 Keyguide and 15 C&B specimens presented the same characteristics as those printed using the Moon Night printer. Prior to sample printing, a calibration protocol (tolerance test and dimensional accuracy test) was performed using RayWare software. This procedure allowed compensation for resin shrinkage or expansion, thus ensuring dimensional consistency in all printed samples. Each resin specimen, after printing and post-processing (MoonWash 2 and MoonLight 2), was subjected to a mechanical test with a universal testing machine. After breaking the specimen, the flexural strength values were recorded with computer software (Bluehill, Instron Corporation, Canton, MA, USA). According to the results obtained, the printing orientation of the specimens does not affect the flexural strength of the two materials examined. However, at the maximum load, some differences emerged for both materials printed with the Moon Night printer, depending on their build angle. Both light-cured resins tested had a higher maximum load resistance when printed with the newer Moon Night printer. This result could be due to the Moon Night printer’s better construction characteristics compared to those of the Sprintray or to issues related to the dimensional calibration of the specimens. Full article

This study investigates the effects of the combined addition of MgO expansive agent (MEA) and rice husk ash (RHA) on the performance of concrete. Results show that MEA absorbs water and competes with superplasticizers for adsorption, reducing early-age fluidity. In the later stages, its reaction with RHA generates M-S-H gel, accelerating slump loss. At early ages (up to 7 days), due to the slow hydration of MEA and partial replacement of cement, fewer hydration products are formed. Additionally, the pozzolanic reaction of RHA has not yet developed, resulting in the low early strength of concrete. In the later stages, Mg(OH)₂ fills pores and enhances compactness, while the pozzolanic reaction of RHA further optimizes the pore structure. The internal curing effect also provides the moisture needed for continued MEA hydration, significantly improving later-age strength. Moreover, in the post-cast strip of a tall building, the internal curing effect of RHA ensures the effective shrinkage compensation by MEA under low water-to-cement ratio conditions. The restraint provided by reinforcement enhances the pore-filling effect of Mg(OH)₂, improving concrete compactness and crack resistance, ultimately boosting long-term strength and durability. Full article

In order to shorten the curing time of the cement-treated aggregate base, provide a stable paving base for an asphalt mixture, and finally, achieve rapid traffic reopening during the maintenance of the pavement (milling and resurfacing of the base layer), sulphoaluminate cement (SAC) was used to prepare cement-treated aggregate with high early strength. As a result, the SAC was first optimized by adding several cement admixtures (i.e., polycarboxylic water reducer, borax, lithium carbonate, and calcium formate) based on hydration kinetics, setting time, compressive strength, and morphology tests. Then, the optimized SAC was used to prepare the sulphoaluminate cement-treated aggregate (SACTA). The test results show that the addition of compound retarder and compound early strength agent in SAC could delay the hydration, reduce microcracks, and ensure required setting time and high early strength. Compared with ordinary Portland cement-treated aggregates (OPCTAs) with the same cement content, the 1 d unconfined compressive strength and indirect tension strength of SACTAs increased by 87.7–184.6% and 133.8–263.6% respectively. The SACTA had smaller total drying shrinkage strain and better anti-scouring performance than OPCTA when using the same cement content. Besides, the 1 d interfacial bonding strength between SACTA and OPCTA was 0.18 MPa, which was higher than the indirect tension strength of OPCTA. The findings in this study indicate that the prepared SACTA could be used for rapid traffic opening during road maintenance. Full article

Tire shape prediction presents significant engineering challenges due to the complex behavior of cord-rubber composites during manufacturing processes. Fabric cord components undergo thermal shrinkage and permanent deformation that substantially influence final tire dimensions, creating discrepancies between mold geometry and cured tire shape. While Post-Cure Inflation (PCI) helps control these dimensional changes, accurate prediction methods remain essential for reliable performance forecasting. This study addresses this challenge through a systematic experimental characterization of fabric cord behavior under manufacturing conditions. Thermal shrinkage and permanent set were quantified under various combinations of in-mold strain and PCI force, with distinct patterns identified for different cord materials (PET and nylon). Based on these experimental findings, a comprehensive finite element analysis methodology was developed to predict cured tire shape. Validation against 65 tire profiles demonstrated remarkable improvements over conventional approaches, with dimensional error reductions of 54.2% for the outer diameter and 49.5% for the section width. Profile and footprint predictions also showed significantly enhanced accuracy, particularly in capturing geometric features critical for tire–road contact characteristics. The proposed methodology enables more precise tire design optimization, improved performance prediction, and reduced prototype iterations, ultimately enhancing both product development efficiency and final tire performance. Full article

Mineral admixtures exhibit significant enhancement effects on the seawater corrosion resistance of sulfoaluminate cement (SAC). This study systematically investigates the influence mechanisms of fly ash (FA), silica fume (SF), and slag powder (SP) on the physicochemical properties of SAC-based materials. Experimental results demonstrate that FA effectively enhances the fluidity of fresh SAC paste while mitigating drying shrinkage. Under standard curing conditions, the compressive strength of SAC mortar decreases with increasing FA content, reaching optimal performance at a 5% replacement level. However, in seawater immersion environments, FA undergoes chemical activation induced by seawater ions, leading to a positive correlation between mortar strength and FA content, with the 10% replacement ratio demonstrating maximum efficacy. SF addition reduces workability but significantly suppresses shrinkage deformation. While exhibiting detrimental effects on flexural strength under standard curing (optimal dosage: 7.5%), a 5.0% SF content manifests superior seawater resistance in marine environments. SP incorporation minimally impacts mortar rheology but exacerbates shrinkage behavior, showing limited improvement in both standard-cured compressive strength and seawater corrosion resistance. Orthogonal experimental analysis reveals that SF exerts the most pronounced influence on SAC mortar fluidity. Both standard curing and seawater immersion conditions indicate FA as the dominant factor affecting mechanical strength parameters. The optimal composite formulation, determined through orthogonal combination testing, achieves peak compressive strength with 5% FA, 5% SF, and 5% SP synergistic incorporation. Full article

Superabsorbent polymers (SAPs) are widely employed as an internal curing agent to enhance the durability and shrinkage–cracking resistance of concrete. However, while its macroscopic effects on concrete properties (e.g., strength reduction) have been documented, the nanoscale mechanisms governing the mechanical behavior of calcium silicate hydrate (C-S-H) gel in SAP-modified concrete remain poorly understood. This knowledge gap limits the optimization of SAP content for balancing durability and strength, a critical challenge in high-performance concrete design. In this paper, we address this scientific problem by combining experimental characterization and molecular dynamics (MD) simulations to systematically investigate how SAP-induced pore structure modifications dictate the mechanical performance of C-S-H gel. First, we analyzed the effects of SAP on concrete pore structure and compressive strength, revealing its role in refining capillary pores into gel pores. Next, MD simulations were employed to construct C-S-H gel models with controlled pore size distributions at three SAP contents (0.2%, 0.3%, and 0.5%), to establish a quantitative relationship between pore characteristics and material performance. The results reveal that pores of ~0.74 nm diameter, predominantly located in weak interfacial regions, critically govern the mechanical behavior of C-S-H gel. At 0.2% SAP content, the C-S-H gel exhibits the highest bulk modulus (10.61 GPa) and optimal mechanical properties, whereas 0.3% SAP leads to a dominant pore cluster at 1.12 nm, resulting in significant reductions in bulk modulus (30.8%), shear modulus (29%), and Young’s modulus (22.3%). These findings establish a quantitative pore-property relationship, providing a mechanistic basis for tailoring SAP content to enhance both durability and mechanical performance in concrete, ultimately advancing the design of longer-lasting infrastructure. Full article

Superabsorbent polymers have been introduced into cementitious materials to solve issues related to early-age cracking, caused by shrinkage, and manual repair. A general improvement of autogenous healing is noticed, while the extent and effectiveness depend on the type of hydrogel and the amount included. To evaluate the self-healing effectiveness, the regain of mechanical performance needs to be assessed. However, such evaluation requires destructive testing, meaning that the healing progress cannot be followed over time. As a solution, air-coupled ultrasonic testing was used within this study, adopting a novel laser interferometer as a receiver, to estimate the regained properties of cementitious mixtures with and without superabsorbent polymers. The sensitivity of ultrasonic waves to the elastic properties of the material under study allows us to monitor the crack healing progress, while the semi-contactless nature of the procedure enables an easy and reliable measurement. Up to 80% recovery in ultrasonic velocity was achieved with reference concrete, while SAP concrete demonstrated up to 100% recovery after wet–dry curing. Following microscopic analysis, up to 19% visual crack closure was obtained for reference concrete, compared to a maximum of 50% for SAP mixtures, for average crack widths between 250 µm and 450 µm. Full article

The durability of concrete is compromised by early-age cracking, which provides a pathway for harmful ions and water to penetrate the material. Early-age cracking, however, is most commonly caused by concrete shrinkage. This study investigates strategies for minimizing the shrinkage of concrete by optimizing aggregate gradation via the Tarantula Curve, reducing cement content, and incorporating lightweight fine aggregates (LWFA) as internal curing agents. The commercially adopted mix design was used as a reference, with the cementitious materials-to-aggregate (C/A) ratio reduced from 0.21 (reference) to 0.15 (proposed), incorporating 0–15% LWFA replacement levels. Workability (ASTM C143), mechanical performance (ASTM C39, ASTM C78), durability (AASHTO TP 119-21), and dimensional stability (ASTM C157) were evaluated through ASTM standard tests. The results highlight that optimizing the C/A ratio cannot only improve both compressive and flexural strengths in regular concrete but also mitigate the total shrinkage by 12.68%. The introduction of LWFA further reduced shrinkage, achieving a 19.72% shrinkage reduction compared to regular concrete. In addition, the sustainability of the developed mix designs is enhanced by the reduced cement usage. A Life Cycle Assessment (LCA) based on the TRACI method confirmed the sustainability advantages of cement reduction. The optimized mix designs resulted in a 30% decrease in CO₂ emissions, emphasizing the role of mix design in developing environmentally responsible concrete. Overall, lowering the cement amount and the addition of LWFA provide an optimal combination of shrinkage control, strength retention, and sustainability for applications. Full article