ABSTRACT High early strength concrete (HESC) has many applications, particularly in the repair and restoration of concrete pavements. These mixtures are designed for rapid strength development using a low water-to-cement ratio (w/cm), specialized cement types (often in higher dosages), and specialized admixtures. Although HESC effectively achieves the required strength, it poses durability challenges. Several studies have explored the effect of these HESC design parameters on strength gain and have provided recommendations to improve it. However, there is limited documentation regarding its durability properties. To better understand HESC’s durability properties, a set of mixtures was analyzed for strength, freeze-thaw durability, and both autogenous and drying shrinkage. These HESC mixtures were composed of low cement content 334.6 kg/m3 (564 lbs./yd3) using ordinary portland cement type III, w/cm of 0.35, three different admixture types, and internal curing (IC) using presaturated lightweight aggregates. It was observed that all HESC mixtures, despite their low cement content, met the criteria established by KDOT Section 833, attaining a minimum compressive strength of 12.41 MPa (1800 psi) and a flexural strength of 2.62 MPa (380 psi) within 6 h of mixing. Furthermore, admixture compatibility and usage of IC for HESC significantly affected their durability properties. HESC with IC demonstrated superior freeze-thaw performance and minimal shrinkage, likely due to their ability to regulate heat during hydration. Although three different admixture types were evaluated for the same mix design and fresh property range, their varying performances emphasize the need to verify admixture compatibility and durability properties before employing them on-field.

Abstract The use of lightweight concrete is gaining prominence in civil engineering because of its effectiveness in minimizing dead loads. However, the increased reliance on concrete has accelerated the depletion of natural resources, raising environmental concerns. This challenge has led to a growing interest in finding sustainable alternatives within the field of civil engineering. This study focuses on the enhancement of bottom ash (BA) to develop a well-graded version (BAW). It examines the impact of replacing fine aggregates with BAW on the mechanical and thermal characteristics of lightweight concrete. The research experimented with different BAW incorporation levels, ranging from 5 % to 35 % by volume. The results showed a consistent decrease in concrete density with increasing BAW replacement, as well as varying changes in mechanical and thermal performance across the tested range of 0–35 % by volume. Mechanical and thermal properties peaked at 15 % before falling. Compressive strength peaked at 36.7 MPa at 15 % and dropped to 26.9 MPa at 35 %. Flexural strength increased to 2.85 MPa at 15 % and 2.57 MPa at 35 %. Split tensile strength increased to 0.76 MPa at 15 % and decreased to 0.63 MPa at 35 %. Ultrasonic pulse velocity reached a maximum speed of 3.86 km/s at 15 % and 3.18 km/s at 35 %. Thermal conductivity increased to 1.67 W/m·K at 15 % and dropped to 1.06 W/m·K at 35 %. The 15 % BAW level optimizes performance, whereas higher replacement rates increase porosity. These findings indicate that well-graded BA enhances the properties of concrete, offering reliable and sustainable material for use in modern construction.

Abstract Shrinkage reducing admixture (SRA), shrinkage compensating admixture (SCA), and superabsorbent polymer (SAP) have been commonly used to reduce shrinkage of high-performance concrete (HPC); however, their comparative effectiveness is still not clear. In this article, the effects of SRA, SCA, and SAP on strength, autogenous/drying shrinkage, restrained ring shrinkage, and pore structure of HPC were studied. The dosages of SRA, SCA, and SAP were varied within 2.5–7.5 L/m3, 2.5–7.5 %, 0.4–1.4 g/kg, respectively. The results indicated that SRA and SCA decreased the shrinkage with their dosages increasing. However, the presence of SAP in HPC mitigated the autogenous shrinkage weakly and raised the free drying shrinkage. SRA, SCA, and SAP all reduced restrained ring shrinkage. SCA was the best admixture to increase compressive strength and reduce shrinkage in HPC. Additionally, the micromechanisms of SRA, SCA, and SAP on shrinkage reduction were addressed based on pore structures. The reduction of mesopore percentage was a primary reason to restrain the shrinkage behavior with the addition of SRA, SCA, and SAP. Moreover, linear fitting models of shrinkages in function of mesopores percentage were proposed. The shrinkage property of HPC could be explained by the mesopores percentage.

Abstract To explore the rheological properties and the modification mechanism of graphene/rubber composite-modified asphalt, a dynamic shear rheometer and low-temperature bending rheometer were used to study the high and low-temperature rheological properties of graphene/rubber composite-modified asphalt. Second, the microstructure and chemical structure of the asphalt were characterized by using Fourier transform infrared spectroscopy and optical microscopy, and the component model of asphalt was constructed with molecular dynamics simulation technology to explore the modification mechanism of graphene/rubber composite-modified asphalt. The results show that compared with rubber-modified asphalt, graphene/rubber composite-modified asphalt effectively improves the high-temperature deformation resistance and low-temperature crack resistance of asphalt, but the ability of graphene to improve the low-temperature performance of asphalt is limited at −24°C or even lower temperatures. The addition of graphene promotes the swelling development of rubber, improves the bonding stability between rubber and resin, and enhances the compatibility between rubber and asphalt systems. Graphene can weaken the aggregation behavior of rubber and asphaltene, and the distribution of rubber and asphaltene in asphalt is more uniform, further improving the overall stability of the asphalt system. Graphene promotes the adsorption of lightweight components by rubber, leading to a decrease in the diffusion coefficients of saturated and aromatic components in asphalt systems. This is also an important reason for the improved high-temperature performance of graphene/rubber-modified asphalt.

ABSTRACT The retro-reflectiveness of the vertical signaling films allows drivers to drive more assertively, directly impacting safety. By collecting retroreflectance (RR) data for 24 months on federal highway BR-381 (Brazilian federal highway – Number 381), in Minas Gerais, Brazil, it was possible to evaluate the RR performance over time of films and the influence of high temperatures from forest fires on the loss of retroreflective capacity. Once the performance equations of the films were determined, the minimum residual RR was verified, certifying the durability foreseen by the standard. Films subjected to burning showed partial or total loss of retroreflective capacity. The films were analyzed in the laboratory, and the degradation was evaluated through accelerated tests at high temperatures. The films were subjected to temperatures of 70°C for 736 h and 100°C for 4 h. It was possible to identify a behavior equation for the films at 70°Cand correlate them to the field study, thus defining a degradation acceleration factor that accurately reflects the natural behavior of the films. Exposure to 100°C was very severe, and verifying a behavioral equation for the process was impossible. Optical microscopy allowed the degradation of the films to be observed as a function of degradation time and temperature. Therefore, degradation at 70°C has the potential to be used as a parameter for accelerated durability testing.

ABSTRACT Previous literature has provided contradictory results, so we present the current investigation to provide additional information to assess the suitability of using soak calcination as a pretreatment method to increase the performance of calcined zeolite when used as the supplementary cementitious material. In this study, natural clinoptilolite zeolite was calcined for three hours at 200°C, 400°C, 600°C, 800°C, and 1,000°C, and the effects of calcination on different physical and chemical properties were observed using a range of experimental tests. The impacts of calcined zeolite were investigated in the hydrated system with the replacement of portland cement up to 20 % by mass on hydration kinetics (i.e., heat of hydration, setting time, chemical shrinkage, degree of hydration), drying shrinkage, and compressive strength. Results revealed that calcination minorly decreased the crystallinity, particle size, and peak pore size of the zeolite, leading to a slightly increased external specific surface area, whereas it increased the rate of moisture absorption and pH of zeolite particles. In the hydrated cementitious system, calcined zeolite reduced the workability and heat of hydration and retarded the initial setting time. The calcined zeolite particles absorbed a part of the water from the fresh mixture and expanded volumetrically, which led to a negative volume of chemical shrinkage up to the final setting time and increased the drying shrinkage. As the dosages of calcined zeolite increased, the compressive strength substantially decreased because of the lower degree of hydration. Overall, soak calcination pretreatment decreased the reactivity of clinoptilolite zeolite particles and impacted the performance of calcined zeolite in the blended system.

ABSTRACT The current research studies the effectiveness of steel fibrous layers on the performance of self-compacting lightweight reinforced concrete two-way slabs with (length/width) ratio ≈ 1.618 (golden ratio). In this work, steel fibers (SFs) have been added to four slab specimens with volume fractions of 0.4 % and 0.8 %, in one bottom layer and two top and bottom layers, in addition to a reference slab without SFs, the four slabs were tested under uniform load. The results revealed that when using single or dual fibrous layers, the flexural strength of slabs was considerably enlarged (numerically 41.3 % for single bottom layer and 72.4 % for both top and bottom layers when using 0.4 % SF, and 113.7 % for a single bottom layer and 193 % for both top and bottom layers when using 0.8 % SF) as compared with nonfibrous slabs, and the failure mode had altered from flexure mode to shear one as compared with nonfibrous slabs. The effect of these fibrous layers was enlarged with increasing the content of SF. And for the same amount of SF, the influence of SF is greater when it is distributed in one bottom layer (numerically 113.7 %) than when distributed in two layers (numerically 41.3 %).

ABSTRACT There is an increasing demand for fine aggregate for use in concrete and mortar. In this study, sand extracted from mine overburden from two locations through the wet-sieving process was used as alternative fine aggregate in mortar. The behavior has been benchmarked with mortar using conventional river sand and coarse and fine sand obtained from crushed stone. Combination mortar with ordinary portland cement and Class C fly ash was used as a binder. The sand-to-binder ratio was fixed as 3, as per ASTM C270-19ae1, Standard Specification for Mortar for Unit Masonry, whereas the fly ash–to–cement ratio was varied from 0.75 to 3. The water required to achieve a constant flow value of 110 ± 5 % was determined. The water retention of fresh mortar and dry density, compressive strength, and drying shrinkage of hardened mortar were determined. Mortar mixtures with sand from mine overburden with a fineness modulus of 2.36 conformed to the water retention requirement of ASTM C91/C91M-18, Standard Specification for Masonry Cement, whereas very fine sand did not satisfy. Masonry mortar with different mixture proportions and fineness modulus of fine aggregate resulted in a range of compressive strengths, satisfying a wide range of mortar designations as per ASTM C270-19ae1, BS EN 998-2, Specification for Mortar for Masonry - Part 2, and IS 2250, Code of Practice for Preparation and Use of Masonry Mortars. For mortar with a fine aggregate of different origins (river sand, crushed stone coarse sand, sand from overburden with fineness modulus 2.67, 3.01, and 2.36, respectively), a marginal variation in drying shrinkage across strength was observed. The maximum drying shrinkage of the higher fly ash–to–cement ratio of the mixture with finer sand was 1,600 microstrain.

ABSTRACT Mineralogical and morphological characteristics of cementitious materials at the early stage of hydration primarily govern the performance and durability characteristics of concrete. Tricalcium aluminate (C3A) is one of the important phases of cement that primarily controls the initial setting. It plays a crucial role in producing tricalcium silicate in the manufacturing of portland cement, which is the dominant phase and is mostly responsible for strengthening and hardening the cementitious system. This necessitates a comprehensive review of C3A hydration, which provides the beneficial role of C3A at the early stage of hydration, and understanding the influence of other admixtures in a modified cementitious system. To this end, this paper presents a critical review of the hydration of C3A and its role during the early stage of hydration. Understanding the reaction mechanism in the presence of various forms of calcium sulfate through different proposed theories has also been critically reviewed. Additionally, admixtures such as accelerators, retarders, water-reducing dispersants, superplasticizers, and parameters like water/solid ratio on C3A grain, which affect the setting time and rheology, have also been thoroughly presented. Furthermore, the role of C3A in the formation of secondary ettringite and the factors that affect the durability of concrete are focused on.

Abstract In construction, additive manufacturing (AM) can be used to create structural or non-structural elements, such as frameworks, reinforcement, or panels. However, AM technology still requires enhancements for the mechanical response of final 3D printed elements to accommodate the mechanical needs of structural components. This paper evaluates various AM process parameters and bioinspired printing patterns to improve the mechanical performance of 3D printed polymeric elements. AM processes, including printing speed and nozzle diameter, are studied. Bioinspired patterns, including Bouligand-like, alternating, sinusoidal, grid, triangular, and hexagonal, are investigated and compared to simple parallel patterns. Results of this study suggest that the mechanical behavior of 3D printed elements can be significantly enhanced by optimizing the printing speed and nozzle diameter. Incorporating bioinspired architectures in AM, such as the Bouligand pattern, are shown to enhance mechanical performance. Slower speeds and larger nozzle diameters result in higher tensile strength. Continuous and twisting patterns yield more ductility, while patterns parallel to the direction of the tensile test result in higher strengths. Microscopic images from the fracture surface indicate that a larger nozzle diameter enhances intra- and interlayer bonding between consequent printed layers. Additionally, more complex crack propagation is observed in twisting patterns with enhanced elongation before total failure. It is also observed that there is an optimal time of exposure to high temperature for deposited materials during AM to improve bonding between adjacent beads. Bioinspired patterns help maintain higher ductility with similar strength despite encompassing higher porosity than parallel patterns, which could be advantageous for material optimization purposes. The bioinspired 3D printed polymeric elements showed tensile properties higher than those of plain polymer filament. The outcome of this study can help optimize both the process and the architecture of 3D printed elements to enhance their mechanical properties to be used as reinforcing elements for reinforced concrete applications.