Introduction Tricalcium silicate(C3S)is one of Portland cement clinker minerals whose proportion is over 50%.It hydrates quickly and releases lots of heat in early hydration period.The reaction rate and degree of C3S in early hydration period are the chelloef constituent to determine the exothermal and mechanical performance of Portland cement;as well as the cracking risk of concrete.One of concrete additive,temperature rising inhibitor,was created to suppress the heat release of binder and decrease its exothermic rate.Cyclodextrin(CD)is the main functional composition of temperature rising inhibitor.It is studied that the effect of CD on the early hydration process of C3S.This work is helpful to understand the action mechanism of temperature rising inhibitor. Methods Pure C3S was calcined,chemical pure CD was used.C3S paste with w/c=0.5 was prepared.The CD dosage in paste is 0%,0.05%,0.10%and 0.20%separately.Dilute C3S solution with the solid content of 10-4 and containing 0,2 mmol/L and 4 mmol/L CD solution was prepared to measure the dissolving rate of C3S in the induction period of hydration.Pore solution of C3S was obtained using centrifugal extraction for fresh paste or press method for hardened C3S paste.The hydration exothermal curves of C3S pastes containing different dosages of CD were measured using isothermal calorimetry.The time-depended concentration variation of Ca and Si in dilute C3S solution and pore solution was measured by ICP-AES.SEM was used to investigate the formation of hydrate nucleus on the polished surface of C3S particles etched by CD solution or pure water.The ion activity product of pore solution relative to C3S was calculated. Results and discussion There is not obvious induction period during the hydration of pure C3S.The induction period of C3S hydration prolongs with the increase of CD dosage in paste.The accumulate heat release of C3S is proportional with its hydration degree.The hydration degree of C3S paste containing CD is higher than blank one at the point of maximal exothermic rate.The accumulate heat release of C3S paste with or without CD is almost same at the end of induction period.The addition of CD decreases the early hydration speed,but does not negatively influence the final hydration degree.CD inhibits momentarily the dissolution of C3S in early hydration period,but does not affects the hydration of C3S in long period.The Ca and Si concentration in pore solution increases with the increase of CD dosage in induction period of hydration.The ion activity product of pore solution relative to C3S is changed when Cd is added into C3S paste.CD is adsorbed at the etch pits on the surface of C3S particles to increase the barrierΔGcrit of the etch pit expansion model and decrease the growing speed of etch pit.There are lots of etch pit on the polished surface of C3S particle after 1 h immersion in pure water.There are few etch pit on the polished surface of C3S particle after 1 h immersion in 1 mmol/L CD solution. Conclusions CD prolongs the induction stage and the main reaction stage of hydration,decreases the reaction rate of C3S.This effect is very intense when the dosage of CD increases to 0.2%.The hydration degree of C3S paste increases in some extent at the peak reaction rate due to the prolongation of the main reaction period of C3S paste containing CD.The ultimately hydration heat release of C3S paste containing CD does not decrease due to the delay of hydration.CD is absorbed on the etch pit of C3S particles in the initial hydration stage to elevate the energy barrier ΔGcrit of the etch pit expansion model.It decreases the dissolving rate of C3S and prolongs the induction period of hydration.In the induction period the exist of CD results in an increase of Ca and Si concentration in pore solution and higher degree of supersaturation relative to Ca(OH)2 and C-S-H.The formation of C-S-H nucleus is inhibited to hinder the acceleration of C3S hydration.

In this study, a boundary nucleation and growth model with a time-dependent growth rate was proposed to quantitively characterize the precipitation of CSH. The newly constructed model was typically applied to quantitively analyse the influence of alkali content on the growth of CSH, and the value-taking equations of the time-dependent growth rate of CSH in various alkali content systems were proposed and verified. The experimental and simulation results proved that a high soluble alkali content stimulated early hydration (within the initial several hours) and inhibited the late growth of CSH (>20 h) in cement paste. The time-varying ion concentrations in cement solutions were the main driving force for the change in the growth rate of CSH with time. Likewise, the variation in the aqueous phase properties of cement pastes also explains the influence of alkali content on the growth rate of CSH, i.e., the high initial pH of the solution with high soluble alkali led to the high supersaturation degree and high growth rate of CSH, consuming large amounts of calcium ions and in turn reducing the later supersaturation degree and growth rate. The newly constructed model is also expected to precisely characterize the factors that have a significant influence on the precipitation of cement hydrates.

Temperature Rising Inhibitor (TRI) is a novel chemical additive used to reduce the early hydration heat of cementitious materials. This study focuses on the influence of dextrin-based TRI on the hydration kinetics of blended cement containing fly ash or GGBS, and the effect of TRI on the reaction of supplementary cementitious materials (SCMs). The effects of TRI are explained by various analysis methods. The results show that the role of TRI on the hydration of cement remains unchanged regardless of the presence of SCMs. But the SCM grains will adsorb a portion of TRI and reduce the efficiency of TRI. According to the TRI adsorption capacity results obtained by TOC measurement, 1 g GGBS grains will adsorb 7.5 mg organic carbon whereas 1 g fly ash grains only adsorb 0.3 mg organic carbon, at the organic carbon concentration of 800 mg/L. Therefore the efficiency of TRI on cement hydration is weakened by GGBS, but barely interfered with by fly ash. The reduction in the hydration degree of blended cements caused by TRI gradually diminishes as the age increases. The "filler effect" of SCMs is still discernible in blended cements in the presence of TRI. A considerable inhibitory effect on the individual reaction activity of GGBS is also observed. The hydration degree of GGBS can be strongly reduced by TRI, which still exists in the long term. Careful consideration should be given to the reduced efficiency of TRI in blended cements containing GGBS, as well as the strong inhibitory effect of TRI on the hydration of GGBS.

Ensuring the repeatability and stability of printing process is significant for the 3D Concrete Printing (3DCP). However, the diversity of printers often leads to unpredictable printing journeys. Hence, in this study the printer head was dimensionally characterized by three factors: channel diameter, neck height, and nozzle diameter. The effects of printer head and process parameters (travel speed, extrusion flow rate, and nozzle height) on the geometry stability and shape of printed filament were investigated with computational fluid dynamics method. The results indicated that, for printing materials without coarse aggregates, extrusion methods had a negligible impact on 3DCP process. For the printer head, the nozzle diameter dominated the geometry stability while the neck height and channel diameter had little effects. A dimensionless parameter was proposed to quantitatively analyze the influences of travel speed, extrusion flow rate, and nozzle diameter. The systematic mechanical analysis indicated that the geometry instability (tearing and meandering) was controlled by the and nozzle height. Based on the above analysis, the selection principle for printing parameters was proposed to ensure a stable and repeatable printing. The research results regarding printer heads and printing parameters can greatly promise the large-scale application of 3DCP.

Graphene oxide (GO) has been used as a functional material in cement-based materials. Most of current research suggests that GO effectively enhance the mechanical properties of cement paste with high water-to-binder (w/b) ratios (0.30-0.50). However, due to the high cost of GO, its use in ordinary concrete materials with high w/b ratios is limited. It has shown promising potential for reinforcement in ultra-high performance cement-based materials with low w/b ratios, such as UHPC. Nevertheless, existing studies have paid limited attention to the effects of GO in cement-based materials with low w/b ratio. This study selected cement-based materials with a w/b ratio of 0.17 as a representative example to investigate the changes in the mechanical properties of hardened cement paste after the addition of GO under different curing conditions. Additionally, by combining the results of microstructural analysis of hydration products, the study explored the mechanism by which GO affects the mechanical properties of cement-based materials with low w/b ratios. The research findings indicate that though an appropriate dosage of GO enhances the compressive strength of cement-based materials with low w/b ratios, it significantly reduces their flexural strength. In addition, GO accelerates the dissolution process of Ca2+ in the early stages, enhancing the degree of cement hydration and increasing the thickness of inner hydration products (IP). This action leads to an increase in the calcium-to-silicate (Ca/Si) ratio and a weakening of the microstructure in outer hydration products (OP). Resultantly, these changes lead to the refinement of small pores and the coarsening of large pores within the hardened cement-based material, collectively manifesting as an improvement in compressive strength and a reduction in flexural strength of the cement paste.

Steel slag has great potential as a supplementary cementitious material, and often shows good effects when used in combination with granulated blast furnace slag (GBFS). In order to reveal the interaction law of steel slag and GBFS, the hydration superposition effect and mechanism were studied in this paper in terms of ion dissolution, hydration heat, hydration products, hydration degree, microstructure and mechanical properties. The results show that steel slag and GBFS have a significant hydration superposition effect, and the strength of the paste when the two are used in combination is much higher. The mechanical properties at the early and later ages are the best (16.5 MPa at 7 days and 31 MPa at 28 days) when the steel slag-to-GBFS ratio is 1:1 and 2:3, respectively. Steel slag-slag composite powder (SSCP) has three exothermic peaks, which are the dissolution peak, hydration peak of steel slag and pozzolanic ash reaction peak of GBFS (after 85 h), respectively. The fibrous and amorphous C-S-H gels and plate Ca(OH)2 appear in the SSCP pastes at 3 days. Furthermore, the microstructure of hydration products consists of a number of fiber-like and particle-like C-S-H gels with widths ranging from 15 nm to 20 nm and lengths ranging from 50 nm to hundreds of nanometers. The C-S-H gels wrap the unhydrated mineral phase (UMP) to form a nucleus(UMP) - membrane (C-S-H) structure. The early hydration of steel slag would increase the pH and conductivity of the pore solution, promoting the dissolution of aluminosilicate glass in GBFS and pozzolanic ash reaction, at the same time, the consumption of Ca(OH)2 by the pozzolanic ash reaction would promote the further hydration of steel slag. The synergistic hydration effect of SSCP would promote hydration and generate more hydration products to fill the pore structure, resulting in good hardening properties.

Temperature Rising Inhibitor (TRI) is a novel chemical addictive used to reduce the early hydration heat of cementitious materials. This study focuses on the influence of dextrin-based TRI on the hydration kinetics of blended cement containing fly ash or GGBS, and the effect of TRI on the reaction of supplementary cementitious materials (SCMs). The effects of TRI are explained by various analysis methods. The results show that within the same TRI to cement ratio, the efficiency of TRI on cement hydration is determined mainly by the TRI adsorption capacity of SCMs in blended cements. GGBS grains have a strong TRI adsorption capacity whereas fly ash grains barely adsorb TRI. Therefore the efficiency of TRI on cement hydration is evidently weakened by GGBS, but barely interfered by fly ash. The impact of TRI on the hydration degree of cement in blended cements gradually diminishes as age increases. The “filler effect” of SCMs is still discernible in blended cements in the presence of TRI. A considerable inhibitory effect on the individual reaction activity of GGBS is also observed. The hydration degree of GGBS can be strongly reduced by TRI, which will continue for the long term. A careful consideration should be given to the weakened effect of TRI in blended cements containing GGBS, as well as the strong inhibitory effect of TRI on the hydration of GGBS.

研究了超细粉煤灰掺量对低水胶比复合胶凝材料浆体流动性的影响,分析了浆体流动性与流变性能的关系.结果表明:在相同水胶比和硅灰掺量下,随着超细粉煤灰掺量的增加,浆体流动度增大,流动时长先缩短后延长,平均流动速率先提高后下降,浆体的黏度系数减小,屈服应力增大,剪切增稠性增强;在相同超细粉煤灰掺量下,浆体的流动度-黏度系数和流动度-屈服应力均呈负相关,黏度系数或屈服应力减小,浆体的流动度增大;在相同流动度下,当超细粉煤灰掺量较高时,浆体的黏度系数减小,屈服应力增大;浆体的流动度同时受其黏度和变形能力的影响.

Ultrafine quartz powder (UQP) can be considered as a kind of physical fillers in concrete production. To improve the environmental efficiency of optimized ultra-high-performance concrete (UHPC), based on Modified Andreason and Andersen packing model (MAA), the UQP was utilized to replace ordinary Portland cement and optimize packing system of UHPC. Subsequently, the physical and hydrated characteristics of UHPC were studied. The results indicate that when UQP is a substitute for Portland cement in the production of UHPC, the influence of its variation content on later age compressive strength of UHPC is difficult to be distinguished. Corresponding to that, the prominent microstructure of the optimized UHPC is developed with high packing density when an optimum addition content of UQP is about 30%. Furthermore, the comprehensive evaluation which is quantified into five indexes (carbon footprint, energy emission, unhydrated clinker, binder and clinker index) demonstrates that the optimized UHPC has a much lower ecological effect in comparison with the majority of UHPC reported in published references, which provides a broad prospect for engineering application of the sustainable UHPC.

The effects of different mineral admixtures on the evolution of static yield stress of common composite cementitious material paste and ultra-high-performance concrete (UHPC)-based paste were investigated. The results show that there are obvious differences in the role of mineral admixtures in the common paste and the UHPC-based paste. Adding mineral admixtures can change the initial static yield stress of the paste by affecting the particle size, particle shape and the charged particles. The addition of mineral admixtures with small particle size such as silica fume and ultrafine slag can increase the initial static yield stress of common paste but reduce that of UHPC-based paste. Adding mineral admixtures changes the evolution of static yield stress of the paste by affecting the particle spacing and the formation and growth rate of hydration products. In turn, the addition of ultrafine slag or silica fume increases the growth of the static yield stress of common paste. Adding slag, fly ash or fly ash microbeads successively reduces the static yield stress of common paste at the later stage. Affected by the content of PCE, the static yield stress of UHPC-based paste containing fly ash microbeads, slag, ultrafine slag and fly ash increases sequentially compared with the blank group at the later stage. The effect of silica fume with different dosages on the evolution of static yield stress of UHPC-based paste is significantly different.

Alkali-activated binder is considered as one of green environmental low-carbon cementitious materials. However, this binder has not been produced commercially and used widely in civil engineering so far. Based on the analysis on the keynote reports on alkali-activated binder in International Conferences on Cement Chemistry, recent work on alkali-activated binder focus on its composition, microstructure of hardened paste and properties. There is a lack of work on building elements and structure made with this binder. This issue hinders the establishment of technical standard system of alkali-activated binder and related design norm of building structure. This could result in a great barrier of the commercial production of alkali-activated binder. As a result, it is rather difficult to enhance the application of alkali-activated binder.

The physical meaning and calculating process of the rheological parameters of two nonlinear rheological models, the parabolic model and the modified Bingham model, were compared. The fluidity test and a rheological experiment on cementitious materials were performed. The Couette inverse problem is a key issue in measuring and solving the rheological parameters of fresh cementitious materials. The solution of the Couette inverse problem based on the modified Bingham model is discontinuous when the coefficient of the quadratic term is equal to zero, resulting in a large deviation between the fitting curve and the rheological experimental data. The credibility of the rheological parameters of the pastes calculated based on the modified Bingham model is low. The formulas for calculating yield stress, fiducial differential viscosity and the degree of shear thickening or shear thinning of the parabolic model have been developed. The credibility of the rheological parameters of the pastes calculated based on the parabolic model is high. The flow performance of the paste can be clearly characterized by the rheological parameters calculated with the parabolic model.

为深入了解含有石灰石粉的复合胶凝材料对混凝土早期性能的影响,研究不同水胶比条件下含有不同比例石灰石粉的复合胶凝材料水化特性,以及所配制的混凝土自收缩和早龄期抗压强度发展规律.研究发现,掺加适量石灰石粉能提高硅酸盐水泥水化放热速率,延长其水化时间.掺加石灰石粉的混凝土在自收缩方面,以12h为分界呈现两阶段发展模式,且收缩值随石灰石粉掺量的增加而增大.混凝土强度随着所用胶凝材料中石灰石粉比例的增加而增大,而石灰石粉活性指数随水胶比增加而线性下降.综合试验中混凝土各性能表现,胶凝材料中石灰石粉的适宜含量≤30％.

通过正交试验研究了水胶比、超细粉煤灰掺量和硅灰掺量对新拌UHPC净浆的工作性与流变性的影响,选取流动度、黏度系数和水膜层厚度为工作性与流变性的衡量指标,利用综合平衡法获得了最优配合比.试验结果表明:水胶比、超细粉煤灰掺量和硅灰掺量的提高都会造成UHPC净浆的流动度和颗粒表面水膜层厚度增大,黏度系数减小;超细粉煤灰掺量是净浆工作性和流变性的主要影响因素,水胶比次之,硅灰掺量的影响最小;UHPC最优配合比:水胶比为0.2,超细粉煤灰掺量为40％,硅灰掺量为8％;以该配合比的成型的UHPC 28 d抗压强度为128.8 MPa,抗拉强度为20.3 MPa,同时满足工作性和力学性能要求,且经济合理.

使用正交试验法，进行用于超高层建筑的大体积底板的大掺量粉煤灰混凝土配合比设计。通过对正交试验结果的直观分析、极差分析、方差分析，得到了配合比中各主要变量对混凝土力学性能的影响规律。试验表明，大掺量粉煤灰混凝土的抗压强度的影响因素依照显著性排序依次为粉煤灰掺量、水胶比和单位立方米胶材用量。大掺量粉煤灰混凝土的抗压强度随粉煤灰掺量和水胶比的升高而降低，胶凝材料用量在合理范围内变动的影响较小。基于各因素的显著性分析结果，给出了混凝土强度和放热性能满足要求的C40混凝土配合比，实际浇筑效果良好。

建立超高性能混凝土(UHPC)浆体的工作性和流变性之间的关系可从理论上研究其工作性变化规律.本文以颗粒膜层厚度为UHPC浆体的工作性的综合衡量指标,设计了正交试验,研究水胶比、超细粉煤灰替代率和硅灰掺量对UHPC浆体的工作性与流变性的影响.根据流动度和流变性测试结果,分析了水胶比和超细粉煤灰替代率的共同作用对UHPC浆体的工作性与流变性的影响,探究了UHPC的净浆与砂浆的工作性关系,基于浆膜层厚度给出了UHPC砂浆的工作性与流变性的关系式.研究结果表明:水胶比是UHPC浆体的工作性与流变性的最主要影响因素,水胶比、超细粉煤灰替代率和硅灰掺量提高均造成UHPC浆体的颗粒表面膜层厚度增大;水胶比和超细粉煤灰替代率的共同作用下,UHPC浆体的流动度和黏度系数具有相关性.

Measurement of concrete creep under constant sustained stress conditions is usually a long process. The external load applied on the specimen may relax gradually during this long process due to the time-dependent properties of concrete and test set-up, which would lead to an improper assessment of concrete creep without considering the stress relaxation effect. This study developed a theoretical method based on the linear superposition principle to derive the specific creep of concrete from the compressive creep test results where a certain amount of stress has relaxed. Three types of high-strength concretes were cast for the creep tests. In addition, the workability, mechanical properties, and shrinkage of the three concretes were measured. Then the application of the existing models including the ACI model, CEB-FIP model, GL2000 model, and B4 model to predict the creep and shrinkage of high-strength concrete was discussed. The results reveal that the specific creep of concrete used in this study without considering the stress relaxation effect decreases by 4.3%∼11.0% when 6.7%∼13.1% of the applied stresses relax during the creep tests. Both creep and shrinkage of high-strength concrete exposed to drying decrease with increasing curing age. It is found that the CEB-FIP model can predict the shrinkage of high-strength concrete well and the B4 model can give a predicted result relatively close to the measured creep of high-strength concrete.

The infrequent setting behavior and hydration process of a Portland cement with very low alkali content were concerned. Gypsum and K 2 SO 4 with different quantities and ratios were added into cement to adjust its sulfate and alkali content. The setting time and compressive strength of cements were tested, the hydration process and hydrates of cements were investigated by isothermal calorimetry, non-evaporable water content and XRD. The results show that gypsum addition is incapable of delaying the quick initial setting of the cement clinker. A moderate substitution of gypsum by K 2 SO 4 in same reasonable sulfate content can promote the dissolution of gypsum, suppress the formation of h-AFm, and therefore prolong the initial setting time of the cement. Moreover, the Portland cement clinker shows a very hysteretic hydration exothermic process, accompanying with a hysteretic finial setting and a weak mechanical property in early age. An appropriate dosage of gypsum can promote the hydration of the cement and result in a reasonable final setting behavior and satisfactory strength development. The modification of gypsum on the properties of cement is influenced by its alkali content. The measures which could accelerate the sulfate-supply in cement is necessary to acquire a favorable hardening property when the cement with low alkali content is used in projects.

The mechanical properties and hydration mechanism of ultrafine ground granulated blast furnace slag powder (UFS)-cement-steel slag powder (SS) ternary cementitious material systems were studied. The chemical effects and contribution ratios of UFS and SS in ternary system at different hydration ages were also investigated. The results show that by adding UFS, the mechanical properties of concrete composites with high-volume SS conforming to the gap-graded particle size distribution are significantly enhanced. The close-packing effect between particles and the pore size distribution of hardened pastes are improved. The strength of cement matrix without any waste is still the highest. The SS has a negative impact on the hydration and strength development of the system at the early hydration ages, but it has a certain promoting effect at later hydration ages. UFS has a visible improvement effect on the hydration and the strength development of the system at both early and later hydration ages. The contribution ratio of UFS was analyzed and was found to be higher than that of SS apparently.

为研究碱含量对水泥水化初期水化硬化特性的影响,利用光学法微流变测量不同碱含量水泥在硬化过程中的黏弹性变化规律,同时测定不同碱含量水泥浆体流动度的经时变化与凝结时间.结果 表明:光学法微流变能准确表征水泥浆体硬化过程中的黏弹性能变化.水泥浆体的黏弹性在拌水20min内急剧增大,之后增长速率减小,维持在基本稳定的状态.碱含量对水泥浆体黏弹性能的影响与水泥凝结时间及流动度变化规律相一致.低碱条件下(＜0.83％ Na2Oeq),随着碱含量的增加,水泥浆体的弹性因子与宏观黏度因子减小,水泥凝结延缓,浆体初始流动度增大;随着碱含量的继续增加,浆体弹性因子与宏观黏度因子由减小转为增大,水泥凝结提前,浆体初始流动度减小.相比于普通水泥,碱含量对低C3A含量水泥的黏弹性能、凝结时间及流动度的影响程度更大.