Steam Curing Research Articles

Health Risks Assessment from Cured-in-Place Pipe Lining Fugitive Styrene Emissions in Laterals

The aim of this study was to improve the understanding of styrene emissions in sewer laterals, resulting from the installation and steam curing of a resin impregnated cured-in-place-pipe (CIPP) liner, within a sanitary sewer. The study included development and performance assessment of a controlled field test program that measures and records styrene emissions before, during, and after steam-curing a CIPP liner. Measured styrene emissions are then compared with those of published studies and regulatory exposure guidelines to assess the potential risk exposure. The field study measurements confirmed that high styrene concentrations can exist in sewer laterals during the steam-curing of the CIPP liner. They also confirm that water, in proper functioning P-traps, will prevent high styrene emissions from exiting the lateral and into buildings. Fugitive emission modeling shows that the risk of exceeding the acute exposure guideline limits is very low, even when high styrene concentrations exist in a lateral with a dry P-trap, and the styrene odor threshold is exceeded within the building, that is, when the building occupants smell styrene.

A comparative study on the properties and environmental impact of mortar with the different paste-to-aggregate ratios under direct electrical and steam curing

Direct (alternating) electrical curing (DEC) is a low-carbon rapid curing method for concrete. However, the interaction between DEC and concrete composition has not been studied. This study makes use of mortar specimens with w/c of 0.4 and various paste-to-aggregate volume ratios (P/A) to examine the effects of DEC and steam curing on the early strength rise rate, late strength development, pore structure characteristics, and environmental impact.The results show that the peak current and temperature increase with increasing P/A under constant curing voltage. The compressive strengths of specimens cured by DEC at 1 d age are greatly improved when compared with specimens cured by standard curing. It is seen that the specimen porosity under DEC is lower than steam curing, the pore diameter is refined, and a dense interfacial transition zone structure exists. It is found that DEC can reduce energy costs by nearly 2/3 compared with steam curing. And the environmental impact index of DEC is only 1/4–1/2 of that of steam curing. In summary, this paper provides am important technical support for the further establishment of DEC regimes.

A time-variant model of chloride diffusion in prestressed concrete cylinder pipe (PCCP) considering the effects of curing age

Chloride penetration is considered as the most responsibility to steel corrosion for PCCP during service. Compared with ordinary concrete structures, the curing method of PCCP is generally steam-curing. Despite numerous contributions have shown that curing age has significant effect on the resistance to chloride penetration of concrete. There is still a lack of critical understanding of the curing age effect on the chloride migration in steam-cured concrete. For this reason, this paper aims to establish a chloride diffusion model suitable for PCCP. In this study, the non-steady-state chloride diffusion coefficient and chloride concentration of steam-cured concrete are measured through RCM test and chloride diffusion simulated test, respectively. The apparent chloride diffusion coefficient and surface chloride concentration are calculated based on Fick’s second law. Moreover, the instantaneous chloride diffusion coefficient was estimated. It is found that the steam-cured concrete cannot ignore the influence of curing age on the chloride penetration resistance, according to RCM test results, the non-steady-state chloride diffusion coefficient of 28 days decreased by 33 % compared with that of 3 days, while the chloride diffusion coefficient of 90 days decreased by 15 % compared with 28 days under steam curing. The larger the curing age, the smaller the chloride concentration at each depth, as well as the chloride diffusion coefficient and surface chloride concentration. In addition, it can be concluded that with the increase of exposure time, the chloride diffusion coefficient decreases gradually, while the surface chloride concentration increases gradually. Thus, the two kinds of test results and theoretical analysis were combined to establish the time-variant models of instantaneous chloride diffusion coefficient and surface chloride concentration of steam-cured concrete considering the effects of curing age and exposure time. On this basis, a new chloride diffusion model considering the effects of curing age, exposure time, the time-variant chloride diffusion coefficient and time dependence surface chloride concentration was established, which plays an important role in durability evaluation of PCCP.

Application of desulfurization gypsum as activator for modified magnesium slag-fly ash cemented paste backfill material

Recycling industrial solid waste for mine backfill is one of the best ways to achieve green production in multiple industries. In this paper, the desulfurization gypsum (DG) as an activator is combined with the modified magnesium slag-fly ash cementitious paste backfill (MFPB) technology for the co-disposal of solid waste and goaf treatment, and the influence of DG on the performance of MFPB was comprehensively analyzed through rheological properties, mechanical properties, durability, microscopic analysis and environmental characteristics experiments. The results show that the fresh MFPB mortar conforms to the Herschel-Bulkley model at different maximum shear rate (γ̇max) conditions. When the γ̇max is 100 s−1, the mortar exhibits shear-thickening properties. The apparent viscosity, yield stress and static yield stress of mortar decreased first and then increased with the increase of DG content, and all had the minimum value when DG was 2.5 %. The thixotropy of the mortar was significantly increased with the addition of DG, and the change in thixotropy was significantly correlated with the difference between the two yield stresses. Both the rheological and mini-slump results demonstrate that DG can improve the flowability of MFPB mortars. In addition, the UCS of D0 under steam curing and standard water curing conditions for 28 d were 4.342 MPa and 2.827 MPa, and the sample containing DG were 6.109–8.241 MPa and 6.669–9.492 MPa, respectively. The addition of DG not only improves the strength of MFPB, but also improves the durability of MFPB. Microscopic analysis (XRD, SEM, and TG-DTG) indicated that this was mainly because DG promoted the hydration reaction of the MMS-FA system and accelerated the generation of C-S(A)-H and AFt. Finally, in the results of in situ leaching based on durability and leaching based on standard HJ 557, all the indexes of MFPB meet the standard of class III groundwater in GB/T 14848-2017, and it has an effective stabilization/solidification effect on heavy metals (As, Cu, Ni, Ba, Zn and Mo, etc.). To sum up, the collaboration of DG and MFPB technology can not only efficiently clean and utilize a variety of solid wastes (MMS, FA and DG), but also greatly improve the performance of MFPB to promote its application.

Behavior of Ultra-High-Performance Concrete with Hybrid Synthetic Fiber Waste Exposed to Elevated Temperatures

The reinforcement of ultra-high-performance concrete (UHPC) with fibers was investigated in this study. Concrete is the most widely used manmade construction material, and UHPC has remarkable mechanical properties. The mechanical properties of UHPC can be modified by a variety of curing procedures and the amount of cement used. This study aimed to examine the impact of fiber reinforcement, temperature, and exposure time on UHPC. Initially, the temperature for UHPC was changed from 300 °C to 500 °C and the exposure time set to 1 and 2 h. Various combinations of the ultrasonic pulse, thermal conductivity, compressive strength, flexural strength, splitting, modulus of elasticity, and drop hammer impact (impact resistance, impact energy, and ductility index) were investigated after 91 days of steam curing. For steam curing, the temperature was kept at 90 °C for three days. The mechanical characteristics of UHPC were the primary focus of this research. The test results showed that the accelerated curing regime achieved a maximum compressive strength of 102.6 MPa for UHPC specimens without fibers and 124.7 MPa for UHPC specimens with fibers, which represents a 22% increase in compressive strength. When compared to UHPC without fibers, all the qualities of UHPC with fibers were improved, especially when subjected to high temperatures. The incorporation of hybrid synthetic waste fibers was a key aspect in developing new ultra-high-strength concrete features.

Compressive Strength Study based on Fly Ash Geopolymer Concrete at the age of 28 days under very High Temperature

Due to creeping process at the burning material, material’s elastic modulus and yield strength will decrease.Three fire protection system are exist in handling the fire problem: active fire protection, passive fire protection, and safety management. In correlation with material problem due to fire, passive fire protection is a strategy to counter it. This paper presents the results of fire protection by using Suralaya fly ash geopolymer concrete. Three molaritas of geopolymer concrete mixture design are 2M, 4M, and 6 M. Sodium Silicate (Na2SiO3) and Sodium Hydroxide (NaOH) are used as alkaline activator. The results of the experiment were analysed by compressive strength for the optimum values. This study found that the value of compressive strength of steam curing is higher than that of water curing, the value of geopolymer concrete compressive strength of 2M is higher than that of 4M, and the value of geopolymer concrete compressive strength of 6M is higher than that of 4M.

Insights into thermal stability and interface bond performance of sisal fiber in ultra-high performance concrete under different curing conditions

It is well known that plant fibers suffer serious alkali hydrolysis and mineralization in ordinary cement mortar or concrete, resulting in significant degradation of interface bond and mechanical performance. The stability of plant fibers in ultra-high performance concrete (UHPC) is seldom reported until now. In this paper, the degradation of sisal fiber in UHPC under steam curing (90 °C) or standard curing (20 °C, RH ≥ 95.0%) conditions were investigated, and the interfacial bonding between sisal fiber and UHPC was also studied. On the other hand, the mechanical properties of UHPC under two curing conditions were carried out. The experimental results indicated that the bonding between sisal fiber and matrix under steam curing conditions was lower than that under standard curing conditions, which was caused by the thermal contraction of sisal fiber at high temperatures. For sisal fibers in UHPC with two curing conditions, thermogravimetric analysis and X-ray diffractometer results revealed that some amorphous substances underwent alkali hydrolyzation and no significant damage occurred on cellulose. The backscattering scanning electron microscope images also showed that the mineralization of sisal fibers in UHPC was very slight. Therefore, the degradation of sisal fiber in UHPC was limited during the curing period and the long-term performance should be further studied.

Effect of steam‒curing on the glass fiber reinforced concrete

Due to the increased need to use precast concrete to reduce construction duration and to accelerate the cement reaction process to achieve the required concrete resistance that enables the elements to gain the required strength to handle the loads generated by the transportation process, many companies use steam curing methods to expedite the hydration process. The steam curing process negatively affects the concrete strength, especially in the long term. Fibers of different types are used to improve the interior composition of concrete and increase its crack resistance. The purpose of the current study was to determine the effect of the glass fiber on the behavior of steam-cured concrete. In this study 90 concrete cubes were used with 15cm dimensions, three different weight ratios of glass fibers (0%, 0.12%, and 0.24%) with two curing methods standard curing in the water tank (water curing - WC) for 3, 7, and 28 days, and steam curing (SC) for 4 and 8 hours. Nine specimens of each mix were cast in 12 mm, and 24 mm fibers length and tested for each curing duration and method. The results of this study indicate that fiber glass addition to the steam-cured concrete has a positive effect on the concrete unit weight and the ultrasonic pulse velocity. Moreover, the result showed that the tensile and compressive strength of the concrete has been positively affected by the length of the fiber more than the fiber weight percentage.

Effect of curing regime on the immobilization of municipal solid waste incineration fly ash in sustainable cement mortar

Stabilizing/solidificating municipal solid waste incineration fly ash (MIFA) with cement is a common strategy, and it is critical to study the high-value utilization of MIFA in ordinary Portland cement (OPC) components. With this aim, binary-binding-system mortar was produced by partially replacing OPC (∼50%) with MIFA, and the effects of different curing regimes (steam curing and carbonation curing) on the properties of the cement mortar were studied. The results showed that the setting time of the cement paste was shorten with the increase of MIFA content, and steam curing accelerated the hardening of the mixture. Although the incorporation of MIFA reduced the strength of the mortar, compared to conventional curing method, steam curing and carbonation curing increased the 3-d strength of the mortar. For high-volume MIFA mortars, the CO2-cured samples had the highest long-term strength and lowest permeability. The incorporation of MIFA increased the initial porosity of the mortar, thereby significantly increasing the carbonation degree and crystallinity of the reaction product - CaCO3. Steam curing also further narrowed the difference in the hydration degree between MIFA-modified sample and plain paste, which may be due to the enhanced hydraulic reactivity of MIFA at high temperatures. Although the incorporation of MIFA increased the porosity of the mortar, this waste-derived SCM refined the bulk pore structure and decreased the interconnected porosity. Additionally, the heavy metal leaching contents of MIFA-modified mortars were all below 1%, which meet the requirements of Chinese standards. Compared with standard curing, steam curing and carbonation curing made the early-age and long-term performance of MIFA-modified mortar better, which can promote the efficient application of MIFA in OPC products.

Synergistic effects of ground granulated blast furnace slag and silica fume on the hydration and compressive strength of extremely low w/b ratio cement pastes

This paper presents results from a comprehensive experimental campaign designed to investigate the synergistic effects of SCMs, specifically, ground granulated blast furnace slag (BFS) and silica fume (SF) on the hydration and compressive strength of ultra-high performance cement pastes (UHPCP). Experiments were performed on 65 mixtures with extremely low w/b ratios (0.16, 0.20) and different SF and BFS replacements under different curing conditions. New insights into the synergistic effects of the SCMs in terms of evolution of portlandite and bound water content, hydration kinetics of UHPCP under standard and elevated curing conditions, and compressive strength are presented. It is demonstrated that effectively controlling the w/b ratio, curing conditions, and importantly the addition of an optimal SF content will favourably influence the hydration and compressive strength of UHPCP. However, the use of high BFS replacement may induce an adverse effect on the hydration and compressive strength of UHPCP. A linear correlation between the bound water content and compressive strength as well as portlandite content is revealed, which serve as valuable indicators for material design. • Underlying hydration mechanisms due to synergistic effects of SCMs are investigated • Synergistic effect by combining SF and BFS improves the strength of UHPCP • Addition of SF to mixtures containing BFS enhances the bound water content • Effectiveness of steam curing is clearly pronounced with higher BFS up to 50% • Good linear correlation between portlandite, compressive strength and bound water

Pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing

Partial replacement of cement with high-volume slag reduces the amount of cement in concrete and thereby lessens the environmental pressure caused by cement production. This paper investigates the pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing, discusses the effects of slag content and pore structure on sulfate attack, and evaluates the methods for determining the sulfate resistance performance. The pore structure results show that the hydration of cement and/or slag reduces the porosity and most probable pore diameter (MPPD) and refines the pore structure of mortars. Steam curing primarily affects the pore size distribution but not the porosity for the mortars within 3 d. Increasing slag replacement increases the porosity for standard-cured and steam-cured mortars at the age of 28 d; however, it significantly reduces the air voids that are detrimental to sulfate resistance. Sulfate attack results show that the combination of the flexural strength test with the sulfate-ion content can evaluate the sulfate resistance well. The sulfate resistance improves with increasing slag content, and 70% of slag improves the sulfate resistance significantly for both standard-cured and steam-cured mortars. In addition, the MPPD, gel pores, and mesopores do not seem to determine the sulfate resistance. Reducing the volume fractions of large capillary pores, especially air voids, can improve sulfate resistance.

PC(Precast Concrete)생산품질 확보를 통한 안전관리 개선에 관한 연구

On 16th of November 2021, the PC slab had been fallen out and dropped to approximately 10M downstairs slab during the PC slab concrete pouring work on the rooftop floor of new logistics warehouse construction in Hwaseoung, Gyeonggi-do, and this accident was mainly caused by the bending fracture of concrete since the weaker strength of the upper compressed concrete compared to the tensile strength of central lower parts failed to withstand the high stress of upper topping concrete pouring. For the investigation of root-cause for above mentioned accident, the design compressive strength had been tested by utilizing the core sampling(extracting) method for the PC slab which was fallen out while pouring topping concrete, and as a result, the average compressive strength of three(3) concrete specimens collected from the relevant member through the destructive test was observed as 21.7MPa (No.1 – 20.6MPa, No.2 – 18.1MPa, No.3 – 26.5 MPa) which is only 55% level of the design compressive strength of 40MPa. The main cause that the average compressive strength was observed at about 55% level of the design compressive strength of 40MPa is the failure to comply with the required standard/specification for steam curing during the PC production processing. The required conditions to be complied for the steam curing are 60±10℃(Max. 80℃ or less) of curing temperature, 20℃/h or less of temperature rise rate and shall be managed by the concrete maturity, however, it was reported as a result of investigating the PC manufacturer that the strength had not reached to the standard strength before the mold deformation due to the steam curing with low temperature condition at opened space. The logistics warehouses have been continuously requested to be expanded after COVID-19 Pandemic, and the demand of PC which has merit in logistics warehouse construction work has been rapidly increasing. As a result, the operation rate of PC manufacturers currently reaches the maximum production limit, instead, PCs have been indiscriminately produced at small workplaces which have not able to satisfy the design compressive strength, construction quality and safety requirements. In the current situation, the construction site and workers are exposed to the potential risk of falling accidents since any relevant law or regulation on non-securing quality requirements such as the compressive strength is not stipulated yet. For this reason, the PC products with secured quality requirements shall delivered and construction safety management shall be improved by implementation of PC Factory Certification System at the earliest. For the purpose of this study, the PC factory certification system should be introduced, the research method was selected based on PC drop accidents and domestic and international operational cases of each country's certification system.

Production of concrete pipes by carbonation curing in an inflatable enclosure

Production of concrete pipes using ambient pressure (AP) carbonation curing in an inflatable enclosure was studied. The process was developed to replace traditional steam curing in order to reduce energy consumption, improve concrete performance and sequester carbon dioxide in pipes. The ambient pressure carbonation was compared with high pressure (HP) carbonation at 5 bar and normal hydration references. A composite structure of calcium carbonate with CSH was found in concrete after AP carbonation. Multiple techniques including quantitative X-ray diffraction analysis (QXRD), thermogravimetry analysis (TGA), Raman spectroscopic analysis, and scanning electron microscopy (SEM) were applied to characterize the strength development and microstructural enhancement of such cementitious matrix. The results demonstrated that AP carbonated pipes had comparable CO2 uptake, three-edge-bearing test (TEBT) strength, absorption, and resistance to internal-hydraulic pressure with HP carbonated ones. In addition, AP carbonation provided nucleating sites for CSH gel growth, thus contributing to the improved performance of concrete pipes while sequestrating CO2 and reducing the overall carbon footprint. Lastly, the carbon sequestration cost is lower in AP than in HP carbonation, which confirms the economic benefits of using AP in early-age carbonation curing of cement-based products.

Optimization Effect of Metakaolin on Macro- and Micro-Mechanical Properties of Composite Cementitious Materials under Different Curing Conditions

To provide the theoretical basis for the engineering application of metakaolin as aluminum-rich pozzolanic ash materials, the promoting effect of metakaolin on the macro- and micro-mechanical properties of composite cement-based composite materials was explored under high-temperature steam and standard curing conditions. Analysis techniques, which involved thermogravimetric and nanoindentation coupled with scanning electron microscopy-energy dispersive X-ray spectroscopy, were used. To analyze the experimental data, the ACI empirical formula and the copula function were used. The correlation among the hydration degree of the MK-cement cementation system, the Al/Si of the C-(A)-S-H phase, and the nanomechanical properties of the C-(A)-S-H gel phase was investigated. According to prior research, the macroscopic mechanical properties and the substitution rate of the MK-cement composite cementitious system can be improved under high-temperature curing conditions in a short period, in which the optimum substitution rate of metakaolin is 20%. The ACI empirical formula was used to demonstrate the functional relationship between the metakaolin replacement rate, curing time, and compressive strength. The MK-cement cementation system can eliminate the defect phase, reduce the CH phase content, and then increase the C-(A)-S-H gel phase content and bulk density. The micro-mechanical properties of the C-(A)-S-H gel phase rises due to its phase content and Al/Si ratio. Furthermore, the copula function verifies the dependence of the nanomechanical properties of C-(A)-S-H gel and Al/Si.

Effect of Steam Curing Condition on Strength and Water Absorption Properties of High Strength Green Concrete

The high-strength concrete could be achieved by using the clinker with the incorporation of cementitious material such as GGBS. However, the use of GGBS as a partial replacement for OPC could retard the strength performances at an early age due to the slow reactivity of slag. In the precast industry, the minimal initial strength of concrete is the most important factor for the demolding of concrete elements. Thus, the improvement on the early strength could be made by using the thermal treatment (steam curing) and a combination of GGBS with highly reactive material such as RHA. In the present study, the performance of pozzolanic and cementitious products was evaluated through the compressive strength and water absorption rate. The results show that the mixture which consists of 40 wt.% cement used with blended GGBS and RHA at ratios of 50, and 10 wt.%, respectively, performed better under the steam curing regimes. The inclusion of RHA-GGBS as a partial replacement for cement could provide a synergic effect by improving the compressive strength value and giving a low water absorption rate of the high-strength concrete.

A Study on Hydrated Phases of Ternary Blended Binder via Thermal Analysis

Replacing the cement content with alternatives material such as GGBS is a wonderful way to solve the issues of environmental degradation caused by cement manufacture. However, the concrete produced using GGBS has some drawbacks such as lower initial strength and higher dry shrinkage. Thus, the ternary blended binder replacement was proven to improve the properties of concrete due to its synergistic effect. RHA is an agricultural waste achieving broader awareness because of its considerable impact on the microstructural properties as well as improving the strength of the concrete. Therefore, in this study, cement as a primary binder containing high-volume GGBS was prepared with RHA via adiabatic temperature (steam curing) and normal curing conditions. The effects of increasing the amount of RHA pre-treated as replacement level of the primary binder with 5%, 10%, 15%, and 20%, with a constant amount of GGBS (50% of slag) were characterized using thermogravimetric analysis (TGA/DTA). The findings showed that RHA reacted as a filler and can be used as a secondary source of SiO2 in cement containing high-volume GGBS production. The inclusion of 60% replacement of RHA-GGBS improves the CSH gel due to CH consumption with SiO2 which is more prominent in long terms ages.

Combined effect of silica fume and fly ash as cementitious material on strength characteristics, embodied carbon, and cost of autoclave aerated concrete.

Aerated concrete (AAC) or lightweight concrete is primarily used for non-load bearing structures in construction work. Generally, it is produced with cement as a main binding ingredient, and the production of cement is blamed to contribute 7 to 8% of CO2 emission in the environment. In addition, the dumping of industrial wastes is also a great environmental concern. This research is an attempt to produce low-cost and sustainable aerated concrete utilizing silica fume and fly ash as partial substitution to cement without compromising the fundamental properties of aerated concrete. The current study was divided into two phases: in the first phase, the silica fume was substituted up to 20% with a variation of 5% in each mix. In the second phase, the fly ash was replaced with cement in three variations, i.e., 10%, 20%, and 30% containing an optimum proportion of silica fume obtained in phase 1. The aluminum powder was added at 0.4% by weight of binder to introduce aeration in concrete. Before testing, samples of aerated concrete were cured with steam in an autoclaving machine for 9h at a pressure and temperature of 1.5 bars and 127°C respectively and oven-dried at a temperature of 105°C for 24h after steam curing. From the experimental results, the highest compressive and split tensile strength of AAC was recorded when 15% of the cement was replaced with silica fume and 30% of the cement was replaced with fly ash combined. At this proportion the least density was also recorded which showed the lightweight of AAC without compromising the strength characteristics. In addition, the reduction of 42.64% and 32.4% of embodied carbon and cost was observed respectively.

Impacts of microwave on hydration evolution of Portland cement in the perspective of composition and microstructure of hydrates

Effects of microwave curing on the hydration evolution of Portland cement were analyzed, compared with normal curing and steam curing. Hydration products, microstructure of cement paste, and the underlying mechanism were investigated. Results showed that the hydration degree of Portland cement under microwave curing for 45-min radiation was higher than that under steam curing at 80 °C for 4 h and normal curing for 12 h. Steam curing promoted the hydration of C3S, and microwave curing accelerated the hydration of C2S. The main hydration products of C3A under normal, steam, and microwave curing, were AFt, katoite, and AFm, respectively. Microwave curing reduced the content of portlandite (CH), decreased the normal size of the face (001) of CH, and increased the preferred orientation of CH. In comparison with steam curing, microwave curing generated granular C–S–H gel with a high Ca/Si atom ratio in hydrated Portland cement.

Experimental and numerical research of ultrahigh performance concrete layered shell element based on a two-dimensional fixed crack model

Ultrahigh performance concrete (UHPC) is a cement-based material with superior characteristics including tension strain-hardening and multi-cracking, which is attractive for application in the field of assembled structures. However, a reliable method for simulating the mechanical behaviour of UHPC structures is lacking. Thus, this study proposes a two-dimensional fixed crack constitutive model for UHPC using the MSC.MARC software based on the experimental results, which is expected to offer high reliability. The stirrup restraint effect, tensile strength hardening, stiffness degradation, and the tension–compression softening of UHPC were considered in the constitutive model. To calibrate the relevant parameters of the constitutive model, UHPC prism and dog-bone specimens with different steel fibre contents were fabricated. Through uniaxial compressive and tensile tests with different loading regimes, the effects of steel fibre content, maintenance mode, and the loading regime on the uniaxial mechanical properties of UHPC were analysed. The test results showed that the peak compressive strain of the specimen with 2% steel fibre content was significantly higher than those of the specimens with 1% and 3% steel fibre content. Furthermore, UHPC exhibits strain hardening and ductility in the tensile experiments. The steel fibre content and steam curing significantly improved the tensile strength of the UHPC specimens. Based on the test data, the skeleton curves and hysteresis criteria of UHPC under compression and tension were proposed, and the formulae describing the process of unloading and reloading, which can be used for the basic constitutive model of UHPC, were fitted. Finally, five UHPC shear wall specimens were designed and simulated through the proposed model. The numerical results obtained using the proposed constitutive model and modelling methodology, including the skeleton curves, failure modes, ductility, and the deformation capacity of the UHPC shear walls, agreed significantly with the experimental results, confirming the reliability and high accuracy of the proposed UHPC constitutive model, thereby increasing the applicability of UHPC.

Experimental Study on the Application of Cementless Material with Industrial By-Products to Steam-Cured Precast Concrete Products.

The purpose of this study was to apply a cementless binder using industrial by-products (fly ash, ground-granulated blast furnace slag, and silica fume) to precast concrete products. In this binder, calcium hydroxide was included as an alkali stimulant but Portland cement was not included. Experiments on the compressive strength and durability of this type of material were conducted and its applicability to precast concrete products was investigated using full-scale specimens. The experiments proved that high-temperature steam curing is effective at obtaining strength development and that compressive strength can be expressed as a linear function of the binder-water ratio. Experimental results of chloride ion diffusion coefficient and sulfuric acid resistance suggested that the proposed material has higher resistances than conventional cement concrete against these deterioration factors. It was also demonstrated that full-scale specimens of a box culvert and a centrifugally compacted pipe using this type of material have almost the same load-bearing capacity and deformation performance as those using conventional cement concrete. It is believed that the proposed material could be used as a construction material instead of cement concrete, contribute to reducing CO2 emission, and increase the reuse of industrial by-products.