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The rapid development of subway and prefabricated building industry, along with the adoption of the "dual carbon" strategy, have put forward higher demands on early strength, environmental protection and high efficiency for precast concrete products and concrete segments. In this study, a ultra-early strength type polycarboxylate superplasticizer (ES) was synthesized successfully by a design molecule structure such as introducting ultra long polyoxyethlene side chains, functional monomer (2-acrylamide-2-methylpropanesulfonic acid), and cationic monomer (Methacrylatoethyl trimethyl ammonium chloride) composition. Discovered through performance testing, the dispersion capacity of ES firstly are increased and then decreased with increasing the acid-ether ratio, and the same trend as the compressive strength harden concrete with ES at the age of 1, 3, and 7 days. The sulfonate groups and cationic monomers into molecular structure, they have little effect on the dispersion capacity, but the compressive strength of concrete at the age of 1, 3, and 7 days get improved. Through camparative study in the setting time of concrete and compressive strength of concrete between ES and an engineering application product SX. The results show that addition of ES does not retard cement hydration, and accelerates the coagulation of cement. Moreover, the compressive strength of concrete is better than SX at all ages, its further verified with X-ray diffraction and Scanning electron microscopy. This study indicates that rational design of molecular structure through the introduction of ultra-long side chains and functional monomers can maximize the early strength performance of polycarboxylate superplasticizer without affecting later strength development. [ABSTRACT FROM AUTHOR]

Expanded polystyrene (EPS) concrete is a new typical composite concrete, but its material toughness and hydrophilicity are poor, leading to low strength and poor toughness. To solve this critical issue, this study used an interactive method of experimentation and simulation to systematically study the mechanism of how the synergistic strengthening of styrene–butadiene latex (SBL) and polyvinyl alcohol (PVA) fibers improves the performance of EPS concrete from the macro, micro, and nano multiscale systems. Macromechanical tests showed that the mechanical properties of EPS concrete are obviously improved by adding PVA and SBL. PVA fiber can reduce the compressive strength of EPS concrete but increase the flexural strength. The addition of SBL has a positive effect on the anticompression and flexural properties. Observation and analysis of microexperiments using electron microscopy, X-ray diffraction, and infrared spectroscopy showed that the addition of SBL improved the weak interface zone, increased the hydration crystallinity of unhydrated cement products, and formed a more abundant cement-based gel to fill weak cement pores, resulting in a more uniform and stable internal structure. At nano scale, the molecular dynamics interface models of EPS/calcium silicate hydrate (C-S-H), EPS/SBL/C-S-H, PVA/C-S-H, and PVA/SBL/C-S-H were established and simulated and analyzed at the nanoscale. The results showed that the addition of SBL played a crucial role in connecting organic polymers with inorganic silicates in a "bridge" form. It formed numerous hydrogen bonds and ionic bonds with EPS, PVA molecular chains, and C-S-H, effectively stabilizing the crystalline layer structure of hydrated calcium silicate and compensating for the weak hydrophilicity of EPS particles, making the EPS/C-S-H and PVA/C-S-H systems more tightly stable. Practical Applications: Expanded polystyrene (EPS) foam concrete, with its advantages of ultralightweight, easy construction, and environmental friendliness, has been widely used in the construction industry. It finds applications in load-bearing precast concrete components, thermal insulation boards, cushioning or structural insulation boards, composite floors, pavement substrates, building envelope structures, and offshore floating structures, among others. These structures possess high strength, excellent insulation performance, high fire resistance, good water repellency, affordability, and strong sound absorption and noise reduction capabilities. However, the hydrophobic nature and porosity of EPS material result in uneven stratification and segregation during the preparation of EPS particles, as well as the existence of numerous weak interface transition zones between EPS and cement-based materials. In order to further expand its prospects in engineering applications and meet the requirements of modern engineering, it is necessary to enhance the workability and mechanical performance of EPS concrete. This study combines experiments and simulations to investigate the mechanisms and methods for reinforcing EPS concrete from a multiscale and multiangle perspective, providing references for the preparation of more stable and high-performance EPS concrete. [ABSTRACT FROM AUTHOR]

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Beam-column joints are crucial load transmission zones because they face concentrated forces from both the beams and the columns. High shear and axial stresses caused by these concentrated forces in the area of the joint may result in decreased joint strength. This article proposes a new beam-to-column connection developed for precast concrete-resisting frames. Concrete mixtures are enhanced mechanically by adding nano silica as it increases compressive strength, flexural strength, and abrasion resistance. Within the concrete, it creates a solid, gel-like matrix that fills voids and strengthens the whole construction. In this study, three reinforced concrete beam-column joint specimens were cast with fly ash, the other three with nano-silica and fly ash, and one sample with nano-silica and a control mix without admixtures was cast. Specimen cast using fly ash and nano-silica is subjected to cyclic loading after 28 days of curing. A load capacity of 100 kN was imposed on the column during testing. It was observed that a gradual increase in fly ash decreased the compressive and flexural strength of the beam-column joints. This decrease in strength was addressed by adding 2.5% nano-silica. Nano silica acts as a nucleus to bond tightly with cement particles during hydration. The results showed that the flexural strength equivalent to that of a controlled specimen can be achieved by adding nano-silica at 2.5% and fly ash at 60%. The highest loading of 38.1 kN can be applied to the specimen with nano-silica without fly ash. Although a higher axial compression ratio can improve the bearing capacity and initial stiffness, it can also reduce deformation capacity and flexibility. [ABSTRACT FROM AUTHOR]

Precast concrete, cold weather concreting, and the emerging technique of concrete additive manufacturing are applications in which the acceleration of cement hydration plays a critical role. To allow precise control of early cement hydration in these applications, a thorough understanding of the working mechanisms of cement hydration accelerators is required. This study contributes to the understanding of the mechanism by which calcium nitrate (Ca(NO3)2) influences early cement hydration. The influence of Ca(NO3)2 on the hydration of an ordinary Portland cement has been followed by isothermal calorimetry, in situ X‐ray diffraction (XRD), quantitative XRD, compressive strength testing, and the analysis of the pore solution composition. Further, the initial pore solution, the initial phase composition, and the phase composition in the fully hydrated cement have been estimated by thermodynamic calculations to corroborate the experimentally obtained results. The results indicate that Ca(NO3)2, especially at the highest analyzed dosage of 5 wt.%, enhances the formation of ettringite and a nitrate‐containing AFm phase. Furthermore, Ca(NO3)2 accelerates alite hydration. Besides the increased Ca concentration in solution, it has been found that a reduction of the Al concentration in the initial pore solution by Ca(NO3)2 possibly contributes to the accelerating effect of Ca(NO3)2 on alite hydration. [ABSTRACT FROM AUTHOR]

In this paper, the effects of steam curing conditions on concrete properties and microstructural characteristics are reviewed, and technical approaches such as appropriate raw material compositions and curing regimes are explored. Moreover, the environmental effects of precast concrete are evaluated. The main conclusion is that steam curing can improve the early strength of concrete, but thermal damage, shrinkage cracking, delayed ettringite formation (DEF), and other factors cause the later strength to increase more slowly or even deteriorate. Accordingly, it is necessary to undertake methods for improvement: (1) Adopt a lot of high-activity mineral admixture + a few low-activity mineral admixture combinations to ensure that the early strength of concrete meets the standard while allowing the subsequent development of concrete hydration to ensure durability. (2) Control the precuring time and temperature gradient of the concrete to allow the initial structure of the concrete to form. (3) Use effective secondary curing, such as soaking in an aqueous solution of limestone, in addition to standard curing to further improve the compactness of concrete. Moreover, the replacement of cement with less than 30% mineral admixtures in steam-cured concrete should be promoted to alleviate the environmental hazards caused by excessive CO2 emissions. [ABSTRACT FROM AUTHOR]

I Aad i 's active involvement in the I fib i dates back to 1975 when he joined the Dutch member group of the I fib i (in those days FIP). The I fib i Fellows awarded in 2021 are I Carmen Andrade, Milan Kalny, Lionel Linger, Tor Arne Martius-Hammer, Aurelio Muttoni, Theodore Neff, Marisa Pecce, Giovanni Plizzari, Juan A. Sobrino i , and I Spyros Tsoukantas i . The I fib i fellows fulfill the following criteria: (1) they are current I fib i members and have been for the last 10 years; (2) they have embraced the values of the federation, and (3) they have provided continuous outstanding contributions to the development of concrete and concrete structures or to the development of the I fib i through the participation in Task Groups and Commissions or other means. In the I fib i , I V.R. Falikman i is involved in Commission 10 Model Codes activities, Task Group 10.1 "Model Code 2020", AG 13 "Concrete Models", and the I fib i TG 4.5 on "Time-dependent response of concrete". [Extracted from the article]

Grouted dowel connections are widely used to resist tension induced by in-plane straining actions and to provide ductility to precast concrete load bearing wall structures. Yet, such connections have not yet been duly investigated. Current design code and standard provisions treat it similar to a simple bar-in-concrete detail. The present study reports the findings of 22 full-scale tests undertaken to examine the bond behaviour of grouted connections under monotonic tensile loading. The examined test parameters included the bar embedment length, bar material and corrugated duct. Results indicate that grouted connections behave quite differently from the bar-in-concrete model assumed in design codes, primarily due to the confinement mechanism of the duct, which provides restraint to lateral expansion of the grout. Varying the embedment length seemed to affect both the bond stress and slip, but did not influence the failure mechanism of the connections. The experimental results were used to calibrate two well-known bond-slip analytical treatments, predictions of which appear to be in good agreement with experimental results. The experimental and analytical findings provide an enhanced understanding on the behaviour of such connections, highlighting the need for revisions in future relevant design code provisions. [ABSTRACT FROM AUTHOR]

Cylindrical concrete reservoirs are appropriate choice to store liquids such as water, oil, ... etc. The use of pre-cast concrete reservoirs considerably increases the speed and precision of construction. In such reservoirs, the assembly of precast wall and roof panels is carried out in construction site. Nevertheless, because of weakness in connections between the wall panels and also between the wall and the foundation, seismic retrofitting may become essential. One innovative method that was applied for seismic retrofitting of numerous precast cylindrical water reservoirs in New Zealand included surrounding the reservoir wall by high tensile post-tensioning cables. In this paper, analytical modeling of wall and roof panels and post-tensioned cables is carried out using the finite element method to investigate the effect of post-tensioning force magnitude, liquid level in reservoir and position of post-tensioning cable on seismic response of reservoir for various height-to-diameter ratios of reservoirs with a constant volume. [ABSTRACT FROM AUTHOR]

Precast, prestressed concrete is used to construct a variety of structures. The primary Milwaukee area precast supplier chooses to make its product without using any fly ash. The argument is that using fly ash would reduce the early release strength of the concrete mix. This paper shows research to dispute that claim and then illustrates the monetary and environmental savings that could be achieved if fly ash is used as a cement substitute. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effect of ground granulated blast furnace slag on the structural performance of precast concrete beams, evaluating the flexural, shear and bonding performance by using the replacement ratio of the ground granulated blast furnace slag as a variable. The design strength of the concrete was set at 45 MPa in consideration of the characteristics of precast concrete products, and the replacement ratio of the ground granulated blast furnace slag to replace cement was 30 to 70%. The experimental results showed that all specimens had similar behavioral characteristics regardless of the replacement ratio of the ground granulated blast furnace slag. Comparison of the prediction results obtained by ACI 318-19 and EC 2 showed that the mean flexural strength and shear strength were higher than 1.19 and 1.43, respectively, and the mean bond strength was 1.57, satisfying the required performance. Therefore, the experimental results showed that in using the ground granulated blast furnace slag as an admixture for precast concrete, the cement replacement ratio may be increased up to 70% without causing any problems in securing the structural performance. Summarizing the results of the present study, a ground granulated blast furnace slag replacement ratio of 50% or lower may be reasonably applied. [ABSTRACT FROM AUTHOR]

Abstract: There is a growing interest of using recycled crushed glass (RCG) as an aggregate in construction materials especially for non-structural applications. Although the recycled crushed glass is able to reduce the water absorption and drying shrinkage in concrete products due to its near to zero water absorption characteristics, the potential detrimental effect of using glass due to alkali–silica reaction (ASR) in cementitious materials is a real concern. The extent of ASR and its effect on concrete paving blocks produced with partial replacement of natural aggregates by crushed glass cullet are investigated in this study. This study is comprised of two parts. The first part quantified the extent of the ASR expansion and determined the adequate amount of mineral admixtures that was needed to reduce the ASR expansion for concrete paving blocks prepared with different recycled crushed glass contents using an accelerated mortar bar test in accordance with ASTM C 1260 (80°C, 1N NaOH solution). In the second part, concrete paving blocks were produced using the optimal mix proportion derived in the first part of this study and the corresponding mechanical properties were determined. It was found from the mortar bar test that the incorporation of 25% or less RCG induced negligible ASR expansion after a testing period of 28days. For mixes with a glass content of higher than 25%, the incorporation of mineral admixtures such as pulverized fuel ash and metakaolin was able to suppress the ASR expansion within the stipulated limit but the results need to be confirmed by other test methods such as the concrete prism test. The study concluded that the optimal mix formulation for utilizing crushed waste glass in concrete paving blocks should contain at least 10% PFA by weight of the total aggregates used. [Copyright &y& Elsevier]