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• High curing temperature increases early concrete strength, while reduces later strength. • The concrete subjected to thermal curing until the CAFS age exhibits superior 28-day UCS in comparison to concrete subjected to thermal curing for only 3 days. • The strength-maturity model corrected using an empirical formula incorporating the "crossover effect", improved the prediction accuracy of concrete strength. The maturity method is widely used to estimate early-age concrete strength. However, the traditional maturity models exhibit limited predictive capability for late concrete strength under thermal curing conditions due to the influence of the "crossover effect". This study developed a curing scheme for Standard Portland cement concrete in the absence of supplementary cementitious materials at temperatures ranging from 5 °C to 50 °C and analyzed the temperature variations inside thermally cured concrete specimens. The findings reveal that an increase in curing temperature and time between 30 °C and 50 °C and 8 and 72 h respectively led to an increase in the early strength and a decrease in the late strength of concrete, due to the "crossover effect". Additionally, a linear relationship was found between curing temperature and the late strength reduction coefficient. Utilizing this relationship, a modified maturity model that considers the "crossover effect" was proposed, improving the accuracy of predicting concrete strength under thermal curing conditions (with a prediction error of less than 10%). The research outcomes are of significant guiding significance for winter construction by ensuring the quality of concrete, reducing construction accidents, and improving construction efficiency. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of SO 3 dopants on the M 1 polymorph formation and mechanical properties of alite containing a high content of MgO. The structure of the M 1 alite is identified by XRD, high-temperature XRD and TEM analysis. A characteristic XRD pattern of M 1 alite doped with MgO and SO 3 is determined, and TEM results show that M 1 alite has an incommensurate modulated structure feature with 2.4 times the subcell dimension along [ 2 ¯ 1 0] H ∗ and could be expressed as ha ∗  + kb ∗  + lc ∗  + m/[2.4(−2a ∗  + b ∗ )], where m = ±1. The First-Principles method is used to simulate the structure of M 1 alite, and the calculated Delta Cohesive Energy is approximately 11–12 eV between the M 1 and M 3 alite. Quantitative analysis is performed by the Rietveld method. The SO 3 /MgO (mass ratio from SO 3 to MgO) and M 1 % in alite M 1 - C 3 S % M 1 - C 3 S % + M 3 - C 3 S % × 100 % are shown to have a strong linear relationship, which can be defined as M 1 - C 3 S % M 1 - C 3 S % + M 3 - C 3 S % × 100 %  = 24.73 + 108.11 * SO 3 /MgO (%). Mechanical properties results show that appropriate SO 3 dopant can improve the compressive strength of alite containing high MgO while over dosed SO 3 will lead to a contrary effect because of the decomposition of alite. The relationship between M 1 % in the alite and the compressive strengths at different ages is also given. The optimal M 1 % in alite is approximately 68% and the best SO 3 /MgO ratio is approximately 0.43 because the compressive strength could be maximized at each age. [ABSTRACT FROM AUTHOR]

The reinforcement for jointed rock mass using rock bolts has always been one of the most effective and economical geo-structural reinforcing technologies widely used in practical civil engineer projects for a long time. In the field of rock mass engineering, the reinforcement effect of the rock bolt(s) on rock mass is much more obvious due to a large number of natural fractures in rock masses. In this paper, an optimized method using Discontinuous Deformation Analysis for Rock Failure (DDARF) is presented to perform numerical investigations on mechanical property and reinforcement effect of bolted jointed rock mass. In order to verify the effectiveness of the proposed optimized DDARF, laboratory experiments using analog material have also been performed. Experimental results are very favorable with those obtained by the optimized DDARF. Moreover, this numerical method has also been employed to study mechanical property and reinforcement effect of rock specimen with single joint and single rock bolt when the joint and rock bolt have different locations in the specimens. The optimal reinforced location for the rock bolt in the specimen has been obtained through the comparative analysis of reinforcement effects under different conditions. The single jointed rock specimens with two rock bolts have also been numerically simulated and the optimal reinforcing location for the rock bolts has also been obtained. It is concluded that this optimized DDARF would provide an alternative effective tool to investigate the mechanical property and reinforcement effect for bolted jointed rock mass. [ABSTRACT FROM AUTHOR]

• M1 and M3 alite along the same pseudo-hexagonal subcell direction were determined. • A new one-dimensional incommensurate modulation structure was found in M1-alite. • The relationship between SO 3 /MgO and M1 alite content in C 3 S was determined. • Compressive strength of clinker was related to the polymorph and content of alite. This paper explored the structural modulation of alite in cement clinkers doped with high content of MgO and a series amount of SO 3. The effect of alite polymorph on compressive strength had also been studied. The results showed that high content of MgO stabilized M3 type alite while the increase of doped SO 3 could gradually modulated the polymorph to M1 type. M1 type alite had an incommensurate modulation along pseudo-hexagonal subcell [ 2 - 10 ] H * direction while M3 type alite hadn't appeared this characteristic. A new incommensurate modulation was found in M1-type alite along the pseudo-hexagonal subcell [ 01 7 - ] H * direction. Quantitative analysis results showed there was a nonlinear correlation between SO 3 /MgO and alite content in clinkers which could be well fitted by the parabola curve. SO 3 /MgO and M1 alite content in C 3 S ( M1 - C 3 S M1 - C 3 S + M3 - C 3 S × 100 %) showed a linear relationship. The compressive strength of clinkers was affected by both polymorph and content of alite. The correlation between the polymorph, content of alite and compressive strength of clinkers was determined by Multiple linear regression analysis. [ABSTRACT FROM AUTHOR]

• CFRP-to-concrete bonded joints exhibit different failure modes when subjected to fatigue cyclic loading. • Bond-slip relation of CFRP-to-concrete bonded joints under fatigue loading was obtained. • The fatigue damage starts to accumulate when the interfacial shear stress is 0.8 of the maximum interfacial shear stress. Carbon fibre reinforced polymer (CFRP) has been accepted by the construction industry as an excellent material for strengthening reinforced concrete (RC) structures against flexural and shear loads. Behaviour of such CFRP strengthened RC structures under quasi-static loading conditions is well understood. Most of the existing studies on CFRP strengthened RC structures under fatigue cyclic loading are focused on demonstrating the effectiveness of the CFRP strengthening on enhancing the fatigue life. However, bond-slip behaviour, a key behaviour governing the performance of flexural/shear strengthened RC structures using externally bonded CFRP, under fatigue cyclic loading remain largely unknown. This paper presents an experimental study aimed at investigating the behaviour of CFRP-to-concrete bonded joints under fatigue cyclic loading. A novel data acquisition system was developed to obtain the strain distribution along the bond length at required force intervals. Experimental results revealed that CFRP-to-concrete bonded joints under fatigue cyclic loading could fail in many different failure modes including, cohesion failure within concrete, cohesion failure within adhesive, and interlaminar failure within CFRP laminate. Failure mode was found to be dependent on the strength of concrete, type of the CFRP laminate, and loading amplitude. Bond-slip relations under fatigue cyclic loading showed that the fatigue damage initiates when the interfacial shear stress is above 80% of the interfacial shear strength. [ABSTRACT FROM AUTHOR]

There is an increasing requirement to manage large amounts of solid industrial waste, such as red mud (RM) and waste glass sludge (WGS), which pose potential environmental hazards to human health. The purpose of this study was to improve the reactivity of the red mud with mechanical activation. The reactivity was measured by the dissolution efficiency of silicon and aluminium in alkaline solution, the strength index, and the strength of the geopolymer. The optimal condition: WGS addition is 30 wt%; grinding time is 20 min; specific surface area reached 24.65 m2/g; the compressive strength of the geopolymer came to 15.98 Mpa curing for 28 days. XRD, FTIR and XPS were applied to investigate the structural transformation in the process. The environmental characterisation showed a significant leaching concentration of heavy metal(loid)s such as Cr, Zn, Cu, and Mn, which decreases with longer curing periods. The carbon emission results showed that the precursor exhibited enormous potential in energy conservation and emission reduction. The study results demonstrate that cementitious material from two solid waste materials can substantially lower heavy metal leaching values whilst also providing economic benefits. This synthesis pathway can be attained through recycling the two solid wastes, resulting in geopolymers that exhibit potential for a variety of applications. • Incorporating waste glass sludge vastly enhances the distribution of particle sizes. • The dissolution efficiency of Si and Al was enhanced by the inclusion of waste glass sludge. • A greater activity index of RM was observed post-grinding. • All heavy-metals contained in the precursor could reach the leaching toxicities' standards. [ABSTRACT FROM AUTHOR]

• We investigate the capacity of CFRP repaired RC beams under heavy pre-load level. • The results indicated that the CFRP sheets significantly affected increased the flexural capacity and flexural stiffness. • An equation is proposed herein to calculate the flexural capacity of pre-damaged reinforced concrete. This paper presents an experimental study to determine the effectiveness of carbon fiber reinforced polymer (CFRP) sheets as a flexural repair system for reinforced concrete (RC) beams. One reference beam and nine CFRP repaired RC beams under heavy pre-damaged level are designed and tested in this study. The effects of several parameters including pre-damaged level, CFRP sheet layer and reinforcement ratio on failure mode, flexural deflection, moment-curvature relation and stress-strain behavior of CFRP sheet are investigated. In the first scenario, a reference beam is tested to determine load levels that can be used as pre-damaged for the tests. With respect to the second experiment, the test beam is subjected to a pre-damaged load equivalent to 40% or 80% of the yield load of the reference beam, respectively. Two failure modes such as the debonding failure of CFRP sheet and the fracture failure of CFRP sheet are found for the strengthened RC beams. The flexural bearing capacity of strengthened RC beams increases as the CFRP sheet layer or reinforcement ratio increases, while it decreases with the pre-damaged level increases. The decrease of pre-damaged level or the improvement of CFRP sheet layer or reinforcement ratio will decrease the deflection of CFRP repaired RC beams. Considering the effect of pre-damaged level and strengthening layer of CFRP sheet, a reduction coefficient of the CFRP sheet layer and an effect coefficient of pre-damaged level are introduced and then a formula for predicting the flexural capacity of CFRP repaired RC beams under heavy pre-damaged level is proposed and it agrees well with the test data. [ABSTRACT FROM AUTHOR]

• Non bonding electrons are firstly determined and quantified in tricalcium silicates. • Non bonding electrons are in both of the isolated and covalent bonded oxygen atoms. • There are more non bonding electrons in M1-C 3 S than that in M3-C 3 S. • Some substituted cations can increase the number of non-bonding electrons on O atoms. • The beneficial cations substituted in alite are with weak electronegativity properties. Alite is one of the most important phases in cement clinker. It is a solid solution of tricalcium silicate (Ca 3 SiO 5 , C 3 S for short, C = CaO, S = SiO 2) which has seven polymorphs. M1-C 3 S and M3-C 3 S are the most common polymorphs in cement clinker. Much experimental research had identified that cations doping affected the polymorph of alite and the hydration properties of cement clinker. This article systemically investigated the influence of cation doping on crystal structures and electronic structures of M1-C 3 S and M3-C 3 S employed by first-principles calculations based on density functional theory. Non-bonding electrons dispersed on the p orbitals of Oi (the isolated oxygen atoms) and Oc (covalent bonded oxygens in nesosilicate tetrahedrons) in C 3 S were determined and quantified by the integration of partial density of states at specified energy levels. Non-bonding electrons are the most probable electrons that will be transferred when the oxygen atoms suffer from electrophilic attack as minerals contact with water. The results showed that there were more non-bonding electrons in both of Oi and Oc atoms in M1-C 3 S than that in M3-C 3 S, which lead to M1-C 3 S more reactive. The substituted cations with specific valence electrons configurations and weak electronegativity are determined, which will typically increase the amount of non-bonding electrons in the systems generally. These would help to understand how cation doping affected the hydration of alite, and furthermore, improve the quality of cement clinker. [ABSTRACT FROM AUTHOR]

Real service environment has a significant influence on fatigue and durability behavior of the members since the main reinforced concrete (RC) structural members of bridges are served under vehicle loads and environment coupling action. However, environment and loads were considered separately (uncoupling) in traditional durability experiments. This was different from the real service conditions of the main structural members of bridge. In this paper, three groups of RC beams strengthened with carbon fiber laminate (CFL) were tested under three point bending fatigue loads with uncoupled hot-wet environment (Group A: 50 °C, 95% R.H) and coupled environments (Group B: 50 °C, 95% R.H; Group C: 50 °C, 85% R.H) to discover the effect mechanism on fatigue and durability behavior of RC members strengthened with carbon fiber reinforced polymer (CFRP) under environment and fatigue load coupling and uncoupling action. Moreover, the fatigue test results in atmospheric condition at room temperature (23 °C, 78% R.H) in earlier stage were compared and analyzed. The research results have shown that the hot-wet environmental fatigue equation of strengthened beams that being proposed was effective and feasible. Comparing with traditional environment fatigue experiment (uncoupled), fatigue limit of strengthened beams under coupling action was relatively lower (decreased 20%) in high temperature and humidity environment (50 °C, 95% R.H). The higher load level was, the greater the fatigue life decreased. [ABSTRACT FROM AUTHOR]

• Diffusion law of chloride ion in CASC under immersion and wet/dry cycles was studied. • Apparent chloride time-varying model of CASC (C30) was established. • Chloride diffusion in CASC was combined with numerical simulation technology. In this study, the diffusion law of chloride ion in coral aggregate seawater concrete (CASC) (strength = C30) was investigated in order to determine the time-varying law of chloride ion migration and penetration in CASC under two different marine environments (i.e. immersion and wet/dry cycles). By measuring the free chloride ion concentration (C f) and apparent chloride ion concentration (C s) in CASC at different erosion times, erosion modes and erosion depths, the chloride ion diffusion coefficient (D) was determined, and then the chloride ion diffusion model of CASC was developed. Combined with COMSOL finite element simulation software, the chloride ion transport model was verified and improved. The results show that the diffusion law of chloride ions in the two environments conforms to Fick's second law of diffusion, and there was a significant promotional effect on the diffusion of chloride ions for the CASC in the wet/dry cycles environment; the trends of C s and D are consistent with time and conform to the power function relationship. The value of C f calculated by using COMSOL has good correlation with the test results; the curve shape of the numerical data is consistent with the test data, and numerical error is very small, which verifies the accuracy of the model developed in this study. [ABSTRACT FROM AUTHOR]

• Imidazoline(IMDL) was prepared as warm mix asphalt additive. • IMDL has little effect on physical properties of asphalt. • IMDL can reduce the contact angle of asphalt on the aggregate surface. • IMDL can significantly reduce the mixing temperature of asphalt mixtures. • IMDL can improve the high-temperature of asphalt mixtures. The high-quality imidazoline surfactant (IMDL) was prepared via amidation of palmitic acid with tetraethylenepentamine followed by intramolecular cyclization reactions as an additive for a warm mix asphalt (WMA). The chemical properties of IMDL and their effects on the performance of asphalt and asphalt mixtures were studied, and the mechanism of its warm mixing effect was discussed. The results show that IMDL molecules contain typical imidazoline functional groups, and IMDL has little effect on the conventional physical properties of asphalt. Particularly, IMDL does not reduce the viscosity of asphalt effectively; Meanwhile, it reduce contact angle of asphalt on aggregate surface which makes it easier for asphalt to spread on aggregate surface and results in a warm mix effect. Thus, IMDL possesses excellent properties that significantly reduce mixing temperature of asphalt mixtures. With the 0.3 wt% addition of IMDL into asphalt, the reduced mixing and compaction temperature of asphalt mixture approaches 31 °C, which effectively cuts the emissions of asphalt fumes by 43.59% and achieves significant energy savings. Furthermore, IMDL can improve the high-temperature performances of asphalt mixtures with little effect on the water stability. Additionally, the price of self-made IMDL can be half of WMA additive widely used in China. In conclusion, IMDL is a good candidate for WMA with high performance and low cost. [ABSTRACT FROM AUTHOR]

This paper investigated the impacts of sulfate adjustment on strength, hydration and the microstructure of cement with triisopropanolamine (TIPA) to propose the mechanism of early strength enhancement from the microscopic point of view. The results showed that a single addition of TIPA was only good for cement strength promotion on 28 days. While an appropriate sulfate adjustment (∼0.6% in SO 3 ) was effective in enhancing the 1 day and 3 days strengths of cement with TIPA. When more sulfate was introduced, a clear delay in the AFt to AFm conversion and a steady increase of heat release could be observed during the early hydration of cement. QXRD analyses revealed that TIPA was able to promote the hydration of intermediate phases, particularly C 4 AF, resulting in the fast formation of aluminate hydrates. The increased sulfate in cement with TIPA not only stabilized AFt formation but also promoted the silicate reaction in the early stages. SEM confirmed that the single addition of TIPA promoted the formation of coarse AFm clusters filling the pores of hardened cement paste. The increased sulfate restored the formation of fine AFt particles, which further refined the microstructure of the paste. Since the addition of TIPA and the adjustment of sulfate altered the hydration kinetics of intermediate phases, different aluminate hydrates intermixing with C-S-H could also be observed. [ABSTRACT FROM AUTHOR]

• Tertiary colours were introduced to white cement pastes using a digital colouration approach. • Design of Experiments (DoE) was used to quantify the relationship of pigment attributes with colour parameters in CIELAB space. • Eight series of quadratic polynomial models were set up to correlate the L * a * b * values of coloured cement pastes with the pigment types and additions. • Cement-based materials in tertiary colours can be widely applied to various scenarios. A tertiary colour design methodology based on the design of experiments (DoE) is introduced for cement paste in this paper. Different types and dosages of pigments are mixed into white cement to form tertiary colours. The quantitative correlation between the types and dosages of iron oxide pigments and the CIELAB parameters for coloured cement paste is established. The experimental results show that for the given ranges of pigment dosage: 0 ∼ 5% for white, red, yellow, blue, and green pigments and 0 ∼ 3.5% for black pigment, not just the white pigment but the black pigment also plays an important role in affecting the variations in the CIELAB parameters. The additions of red, yellow, green and blue pigments influence the green–red and blue-yellow opponent colours, and an interaction at high levels of addition for a pair of pigments is recognized. With the help of DoE, eight series of quadratic polynomial models were set up to correlate the CIELAB parameters obtained for coloured cement pastes with the pigment attributes. By using this method, tertiary colours can be introduced to cement-based materials that can satisfy the needs of various application scenarios. [ABSTRACT FROM AUTHOR]

• This paper detects the damage of the material under different loads using the ultrasonic velocity test method, and compares and determines the oxygen diffusion coefficients of coral concrete specimens at different loads in the dried state. • COMSOL is used to simulate oxygen diffusion in coral concrete, which is compared with the experimental data. • The damage of coral concrete is greatly influenced by the load. With increasing load, the damage worsens as internal cracks in the coral concrete increase in number, and the observed ultrasonic velocity gradually decreases. • Based on the established model and the numerical simulation of oxygen diffusion in coral concrete using COMSOL, it is concluded that the simulated values exhibit a good correlation with the experimental values. The diffusion law of oxygen in coral concrete under different loading conditions was investigated in this study. Compressive strength of nine groups of C30 coral concrete was measured to determine the ultimate compressive strength of coral concrete. Then, loads of 0, 25, 45, or 65% of the compressive strength were applied, and the damage to the specimens was quantitatively characterized via an ultrasonic method. Further, the oxygen diffusion coefficient of coral concrete was measured under different loads. Next, numerical simulations were carried out by using COMSOL software to verify and improve the oxygen diffusion test of coral concrete. The results show that the damage of the coral concrete increases with increasing load, while the ultrasonic velocity gradually decreases. Owing to its higher porosity, coral concrete exhibits a greater oxygen diffusion coefficient than mortar specimens with the same mix ratio, and the diffusion of oxygen in coral concrete follows an exponential rate law. With increasing pre-applied load on the specimen, an increase in the damage and the number of microcracks of the specimens as well as in the oxygen transmission rate and the final oxygen diffusion coefficient could be observed. The calculated values of the model obtained by using the numerical simulations exhibit a good correlation with the test results, which verifies the accuracy of the model established in this study. [ABSTRACT FROM AUTHOR]

• The humid environment with different rainfall times and rainfall intensity was simulated in the laboratory. • The surface chloride contents showed decreasing trends and were strongly affected by the rainfall parameters. • The convection zone depth and peak chloride ion concentration in chloride profiles was studied. • Numerical simulation of chloride transportation in the humid environment with rainfall was conducted. • A prediction model for chloride transportation under different rainfall parameters was proposed. Reinforced Concrete (RC) structures eroded by chloride ions will reduce the chloride ion concentration on the concrete surface under the effect of sustained rainfall dilution and erosion, and there will be rainfall convection areas and peak chloride ion contents. In this study, the influence of rainfall environment on the transporting behavior of chloride ions in concrete is studied through capillary absorption test and rainfall experiment. A numerical prediction model of chloride ion transporting behavior in concrete was established by COMSOL Multiphysics based on the rainfall tests. The chloride behavior is analyzed and studied. It is found that the numerical simulation results are in good agreement with the experimental results, and the predicted models of chloride ion diffusion under different rainfall conditions are obtained, and the transporting behavior of chloride ions can be effectively predicted. The results also show that with the increasing of rainfall intensity and rainfall time, the chloride ion contents on the concrete surface decreases obviously. When the rainfall time and rainfall intensity increase, the chloride ion contents of concrete decreases, and the binding capacity of chloride ions in the matrix weakens. This research provides some resulting information of RC structures in rainy marine areas. [ABSTRACT FROM AUTHOR]

• The Portland cement clinker was modified in a sintering atmosphere containing SO 2. • SO 2 could affect the content and structure of alite in Portland cement clinker. • SO 2 could change the grain size and micromorphology of alite. • The clinker sintered in SO 2 atmosphere had higher hydration activity. This paper explored the influence of gaseous SO 2 at different temperatures on the composition and structure of the secondary sintered cement clinker. The combination of X-ray powder diffraction (XRD) and rietveld refinement was used to study the composition and content changes of clinker phase. The morphology and clinker sintering history of the clinker phase were determined by the petrographic analysis. The structure of alite was identified by XRD and transmission electron microscopy (TEM) analysis. The experimental results showed that the presence of gaseous SO 2 promoted the decomposition of alite and increased the value of M1-alite%/(M1-alite% + M3-alite%). The hydration exothermic curve showed that the activity of M1-alite was higher than that of M3-alite. [ABSTRACT FROM AUTHOR]

• The rainfall environment was simulated in the laboratory. • The influence of rainfall intensity on the distribution of chloride ions in concrete was studied. • The distribution of chloride ions in concrete under different saturations was discussed. • In this environment, the relationship between total chloride ion and free chloride ion in concrete is analyzed. • The SEM, MIP and XRD phase analysis of the compounds under different rainfall intensities were explored. Reinforced concrete (RC) structures located in coastal salt spray areas are subjected to rainfall erosion and chloride ion corrosion throughout the year. Consequently, this study simulates a rainfall environment with artificial rainfall simulation devices and applies a potentiometer to determine the chloride ion concentration. The microstructures and chemical compositions of the concrete were revealed through microscopic experiments. The research results show that with a greater rainfall intensity, the surface chloride ion concentration decreases more obviously, the surface chloride ion loss is more serious, and the chloride ion binding capacity becomes weaker. As the saturation decreases, the binding capacity of chloride ions also decreases. This study can provide some theoretical ideas for the durability design of PC structures in rainy environments. [ABSTRACT FROM AUTHOR]