Effectiveness of new silica fume alkali activator

The effectiveness of a new type of alkali activator is studied. The activator is a product of silica fume. The results obtained showed the silica fume activator as a highly effective substance for the alkali activation of the combinations of Portland cement, silica fume and blast furnace slag, and slag alone. The positive effect of activator is based on the intensification of the production of calcium silicate hydrates and the densifying of the forming pore structure of the activated binder.     

Characterisation of ground hydrated Portland cement-based mortar as an additive to alkali-activated slag cement

The sustainable development of cement manufacturing requires extension of the raw material base, including large-tonnage waste. Hydrated mortar waste is a promising mineral resource for the production of Portland cements and alternative binders, such as alkali-activated slag cement. The influences of ground-hydrated mortar aged for 3 months on the properties of alkali-activated slag fresh and hardened pastes were performed. The results show that the properties are dependent on the concentration (2.5–60%), cement:sand ratio (1:1–3) and fineness (200–600 m²/kg) of the ground hydrated mortar; the alkali activator (sodium carbonate and sodium silicate); and the curing conditions (normal conditions and steam curing). The fresh paste properties that we considered in this study included the water requirement and the setting time; the hardened paste properties we considered were the water absorption, the density, and the compressive strength after 2, 7, 14, 28, 180 and 360 days of ageing. The ground hydrated mortar improved the early strength and the long-term strength of the alkali-activated slag paste and replaced the slag up to 50%. The factors that affecting the strength of the alkali-activated slag cement with ground hydrated mortar as an additive were, in order of influence, alkali activator type > curing conditions > cement:sand ratio > ground-hydrated mortar fineness.     

响应面方法优化碱激发矿渣-石粉水泥砂浆的研究

基于响应面中的中心复合试验法,选择碱含量和石灰石粉含量作为配合比变量,制备碱激发矿渣-石粉水泥砂浆,并研究其不同龄期的力学强度。通过数据处理得到各变量与抗折、抗压强度的响应曲面,分析了各变量对碱激发矿渣-石灰石粉水泥砂浆强度的影响规律,建立了各龄期强度的响应面模型,为现场不同龄期的砂浆强度预测提供了科学的方法。结果表明,当Na2O含量为8.27%(质量分数,下同)、石灰石粉含量为14.02%时,各组分能充分发挥协同作用,保证良好的力学性能,且响应面法是一种有效优化碱激发水泥砂浆组分的方法。     

钢渣-矿渣基全尾矿充填胶结材料的研究

以冶金废渣钢渣、矿渣及电厂废渣脱硫石膏为主要原材料,添加少量的硅酸盐水泥及激发剂,制备了一种新型的钢渣～矿渣基全尾矿充填胶结材料。通过系统试验,确定了制备钢渣-矿渣基全尾矿充填胶结材料的最优配比及影响其性能的显著性因素。结果表明,采用钢渣-矿渣基全尾矿充填胶结材料制备的充填体在胶砂比为1;9、固体浓度约为68％时,28天抗压强度可达到2．5MPa以上。钢渣-矿渣基全尾矿充填胶结材料的固体废弃物含量高达90％以上,且成本明显低于普通水泥,因此会产生较好的环境和经济效益。     

Micromechanical properties of alkali-activated slag cement binders

An experimental investigation into the micromechanical properties of alkali-activated slag cement (AASC) binders was carried out using targeted and grid nanoindentation. The results of grid indentation techniques were deconvolved using Gaussian mixture modeling with Bayesian model selection to determine the appropriate number of component phases for the model. The information given by the resulting mixture models and from targeted indentation experiments was disseminated in the context of existing information about the composition and development of the microstructure in AASC binders. The microstructure of sodium silicate-activated slag cement contains only two components (ground mass gel and unreacted slag cement) upon microscopic examination, but indentation data suggest that it is much more complex and varied. The microstructure of sodium hydroxide-activated slag cement contains ground mass gel, unreacted slag cement, and an inner product ring surround the unreacted slag. The inner product is denser, harder, and stiffer than the surrounding product phases. The micromechanical properties in sodium hydroxide-activated slag cement are not affected by activator molarity; the macroscale strength is similarly unaffected. Conversely, the micromechanical properties of sodium silicate-activated slag show a slight improvement with increased silica modulus, while the macroscale strength shows a significant improvement. The macroscale improvement is likely due to the increased size of unreacted slag cement grains, which are shown to be very hard and stiff.     

Development of alkali activated cement from mechanically activated silico-manganese (SiMn) slag

Silico-manganese (SiMn) slag has been used to develop alkali activated cement binder. The reactivity of SiMn slag was altered by mechanical activation using eccentric vibratory and attrition mill. The reaction kinetics during alkali activation of SiMn slag and structural reorganization were studied using isothermal conduction calorimetry and Fourier transform infrared spectroscopy. The particle size after milling was smaller in attrition milled samples but reaction started earlier in vibratory milled samples due to more reactivity. This observation was further supported by compressive strength which was highest in samples prepared from vibratory milled slag. The main reaction product was C–S–H (C = CaO, S = SiO₂, H = H₂O) of low crystallinity of different types with varying Si/Al and Ca/Si ratio. An attempt has been made to relate the microstructure with mechanical properties. The results obtained in this study establish technical suitability of SiMn slag as raw material for alkali activated cement.     

Durability assessment of alkali activated slag (AAS) concrete

The environmental impact from the production of cement has prompted research into the development of concretes using 100% replacement materials activated by alkali solutions. This paper reports research into the durability of AAS concrete. The durability properties of AAS have been studied for a range of sodium oxide dosages and activator modulus. Properties investigated have included measurements of workability, compressive strength, water sorptivity, depth of carbonation and rapid chloride permeability. Microstructure studies have been conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy. It was concluded that an activator modulus of between 1.0 and 1.25 was identified as providing the optimum performance for a sodium oxide dosage of 5% and that AAS concretes can exhibit comparable strength to concrete currently produced using Portland cement (PC) and blended cements. However, with regards to the durability properties such as water sorptivity, chloride and carbonation resistance; the AAS concretes exhibited lower durability properties than PC and blended concretes. This, in part, can be attributed to surface microcracking in the AAS concretes.     

Compressive strength of geopolymers produced by ordinary Portland cement: Application of genetic programming for design

In the present study, compressive strength results of geopolymers produced by ordinary Portland cement (OPC) as aluminosilicate source has been modeled by gene expression programming. Six main factors including NaOH concentration, water glass to NaOH weight ratio, alkali activator to cement weight ratio, oven curing temperature, oven curing time and water curing regime each at four levels were considered for designing. A total of 32 experiments were conducted according to the L32 array proposed by the method. The gene expression programming models were constructed by 10 input parameters including NaOH concentration, water glass to NaOH weight ratio, alkali activator to cement weight ratio, oven curing Temperature, oven curing time, water curing regime, water glass content, NaOH content, Portland cement content and test trial number. The value for the output layer was the compressive strength. According to the input parameters in the models, the constructed networks were trained and tested. The results indicate that gene expression programming model is a powerful tool for predicting the compressive strength of the geopolymers in the considered range.     

Understanding the drying shrinkage performance of alkali-activated slag mortars

In this work, drying shrinkage of four alkali-activated slag (AAS) mortars, prepared using various types/dosages of activator, was characterized at four different levels of relative humidity (RH) and two drying regimes (i.e. direct and step-wise drying). The results show that drying shrinkage values of AAS are significantly dependent on the drying rate, as AAS shrinks more when the RH is decreased gradually, instead of directly. At high RH, the drying shrinkage of AAS exhibits a considerable visco-elastic/visco-plastic behavior, in comparison to ordinary portland cement (OPC). It is concluded that the cause of high-magnitude shrinkage in AAS mortar is due to the high visco-elastic/visco-plastic compliance (low creep modulus) of its solid skeleton. Furthermore, the activator affects the shrinkage behaviors of AAS by influencing the pore structure and mechanical properties.     

Influence of alkalis on porosity percolation in hydrating cement pastes

Loss-on-ignition (LOI) measurements and low temperature calorimetry (LTC) are used to study the properties of hydrating cement pastes with various quantities of alkalis. In addition to the well-known acceleration of early age hydration and “retardation” of later age hydration, the alkalis are observed to have a significant effect on the percolation of the porosity in the hydrating systems, as assessed using the LTC technique. At equivalent degrees of hydration, the capillary pores in cement pastes with sufficient added alkalis may depercolate while those in lower alkali cement pastes remain percolated. A simple dissolution/precipitation three-dimensional microstructural model is applied to examine the potential effects of hydration product morphology (random, needles, and plates or laths) on pore space percolation. The model suggests that the observed experimental results could be consistent with the higher alkali levels modifying the morphology of the C–S–H gel to produce more lath-like hydration products, as has been observed by others previously using electron microscopy. Potential implications for the transport properties and durability of these materials are discussed.     

土聚水泥的聚合反应与研究现状

分析了土聚水泥的化学成分以及矿物组成;讨论了其水化产物的形态以及结构特点;概述了土聚水泥具备的性能特点;介绍了土壤聚合反应的机理,指出土聚反应产生的过程是介稳状态的偏高岭土等无定型硅铝化合物在碱性激活剂及促硬剂的作用下经历一个由解聚到再聚合的过程,从而形成类似地壳中一些天然矿物的铝硅酸盐网络状结构;将土壤聚合反应的过程分为5个部分.     

Alkali activation of a slag at ambient and elevated temperatures

Strength development of alkali activated slag (AAS) mortars, activated using alkali hydroxide and sodium silicate, was investigated at room and elevated temperatures. Heat evolution at room temperature was measured using isothermal calorimetry. Important differences were observed between critical activation parameters. Heat cured specimens gain strength rapidly, humid oven conditions being favorable, but given sufficient time room temperature curing yields comparable strengths. Both activators are needed for high strength at room temperature, NaOH solution is more critical and its concentration greatly influences strength. At 80 °C however, sodium silicate is essential and even sufficient. KOH is more effective than NaOH at 80 °C, but not at room temperature. Lower water-to-slag ratios give higher strength at early ages. AAS hydration evolves less heat than Portland cement hydration. Time to significant strength gain of mixtures can be predicted using their time and heat evolution at setting. Twenty eight-day strength of AAS mortars is roughly related to total evolved heat and increases nearly linearly with the amount of NaOH activator for fixed water glass content.     

Elastic properties of cement-stabilised mixes with steel slag

In this study, we evaluated the elastic and mechanical properties of a new type of cement-stabilised material made with steel slag, varying the content of cement and steel slag. To study the elastic properties of these mixes, we measured their density, compressive strength and ultrasound pulse velocity at curing ages of 7, 28 and 90 days. The aggregate type and curing age greatly affected the elastic properties and varied much depending on the cement content. The Poisson's ratio chosen in analyses had little influence on the dynamic modulus. Various expressions given by building codes were used to predict the elastic properties of the mixtures. These codes generated very different values of the static modulus of elasticity, making most of them unsuitable for predicting the elastic properties of cement-stabilised materials. Using our experimental data, we provide the best combination of existing equations to predict elastic properties, and we conclude that measuring the ultrasound pulse velocity is a suitable way to predict the mechanic and elastic properties of cement-stabilised materials.     

Feasible use of large volumes of GGBS in 100% recycled glass architectural mortar

The use of 100% recycled glass as aggregates in architectural mortar is regarded as an environmentally friendly, cost-effective and attractive feature for construction applications due to the natural characteristics of glass (e.g. aesthetic pleasing, impermeability, chemical resistance properties). However, the need to use large quantities of white cement for architectural products may increase the overall cost of production. Therefore, the possibility of using a near-white coloured ground granulated blast furnace slag (GGBS) to replace white cement for architectural mortar production is an attractive option. This paper reports a study which is an extension of our previous work aiming to investigate the feasibility of using large volumes of GGBS (ranging from 15% to 75% white cement replacements) to produce self-compacting-based architectural mortars. To improve the appearance (whiteness) of the mortar, a small quantity of titanium dioxide (TiO₂) was added to the selected mixes for comparison purposes. Fresh and hardened properties of the mortar including mini-slump flow, density, water absorption, flexural strength, equivalent compressive strength, drying shrinkage, alkali silica reaction (ASR) and acid attack resistance were investigated. The overall performance showed that it is feasible to use GGBS for the production of architectural mortar and 60% replacement of white cement by GGBS was determined to be optimal. The replacement significantly increased the flexural strength, and reduced the drying shrinkage and risk of ASR expansion, as well as improved the ability to resist acid attack of the mortar produced.     

锰渣掺合料对砂浆收缩性能的影响

锰铁高炉废渣研磨后,勃氏法测得比表面积为5400cm2/g.磨细锰渣掺合料以15%和30%替代水泥,制作砂浆试件并测试干燥收缩值,同时试验了激发剂对锰渣水泥试件收缩值的影响.结果表明,锰渣掺合料会使砂浆试件的收缩增大,锰渣掺量愈多收缩值愈大.S激发剂促使锰渣水泥砂浆试件早期收缩增大.试验结果对锰渣掺合料用于混凝土结构中的收缩与抗裂性能具有参考意义.     

Carbonation process of alkali-activated slag mortars

This study analyzes the behaviour of waterglass- or NaOH-activated slag mortars after carbonation. The effect of a superplasticizer based on vinyl copolymer and shrinkage reducing polypropylenglycol derivative admixtures on that process was also examined. The same tests were run on cement mortars for reference purposes. The mortars were carbonated in a chamber ensuring CO₂ saturation for four and eight months, after which ages the samples were tested for mechanical strength; mercury porosimetry and mineralogical (XRD, FTIR) and microstructural characterization (SEM/EDX) were also conducted. The results obtained indicate that alkali-activated slag mortars were more intensely and deeply carbonated than Portland cement mortars. Carbonation took place directly on the gel, causing decalcification. When waterglass was the alkaline activator used, carbonation caused a loss of cohesion in the matrix and an important increase in porosity and decrease in mechanical strength. When a NaOH solution was used as the alkali activator, carbonation enhanced mortar compaction and increased mechanical strength. Finally, in waterglass-activated slag mortars, the inclusion of organic admixtures had no effect either on their behaviour after carbonation or the nature of the reaction products.     

Strength and hydration properties of reactive MgO-activated ground granulated blastfurnace slag paste

Ground granulated blastfurnace slag (GGBS) is widely used as a partial replacement for Portland cement or as the major component in the alkali-activated cement to give a clinker-free binder. In this study, reactive MgO is investigated as a potentially more practical and greener alternative as a GGBS activator. This paper focuses on of the hydration of GGBS, activated by two commercial reactive MgOs, with contents ranging from 2.5% to 20% up to 90 days. The hydration kinetics and products of MgO–GGBS blends were investigated by selective dissolution, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy techniques. It was found that reactive MgO was more effective than hydrated lime in activating the GGBS based on unconfined compressive strength and the efficiency increased with the reactivity and the content of the MgO. It is hence proposed that reactive MgO has the potential to serve as an effective and economical activator for GGBS.     

Biological response of new activated acrylic bone cements with antiseptic properties. Histomorphometric analysis

The biological response to an acrylic bone cement cured with 4,4′-bis-dimethylamino benzydrol (BZN) as activator of reduced cytotoxicity and antiseptic properties, has been carried out and compared with that obtained for CMW 3 cement. Histomorphometrical data (undecalcified trichromic Goldner staining) were obtained by measuring the most significant variables at the bone-cement interface. Quantitative results of tissue response revealed that newly formed bone and connective tissue were maximum at 4 weeks whereas bone marrow increased with time of implantation for both cements. Statistical analysis (p < 0.05) showed no significant differences in newly formed bone and bone marrow with time and between both groups, however, connective tissue significantly decreased between 4 weeks and 12 weeks for BZN cement, and between 12 weeks and 24 weeks for CMW3. By comparing both cements at each time, lower significant percentage of connective tissue at the bone-cement interface of the BZN cement, was obtained at 12 and 24 weeks, however, a very low amount of connective tissue was found for both cements. All the results indicate that the new activated system could be applied clinically in a relatively short time, after the corresponding preclinical study.     

Effect of superplasticizers on the rheological properties of cements

In this paper, the rheological properties of cement pastes made with different types of cement and superplasticizers are discussed. As a tool for the discussion, experiments involving dispersion of cement particles, fluidity, viscosity, yield stress and zeta potential have been conducted. The results obtained show that the chemical compositions of the cements such as C₃A and sulfate content, alkali and ground lime content are important features controlling the rheology of cement pastes. Three types of sulfonated superplasticizers (lignosulonate-based, melamine formaldehyde sulfonic acid, naphthalene formaldehyde sulfonic acid) and one type of polycarboxylic acid polymer were used. The results revealed that the mechanism by which these polymers disperse cement particles differs fundamentally. Sulfonated superplasticizers induced a negative charge on cement particles dispersing them by electrostatic repulsion, whereas with the polycarboxylate-based polymer the dispersion mechanism is mainly controlled by steric hindrance. A model for the adsorption of superplasticizer on a cement particle is proposed.     

镍渣/偏高岭土基地聚合物的制备与表征

以工业固体废弃物镍渣和偏高岭土为原料,以水玻璃为激发剂,在相同稠度下制备镍渣/偏高岭土基地聚合物。研究了镍渣种类和掺量对地聚合物力学性能和体积变化的影响,测定了地聚合物的碱溶出情况,并利用XRD、SEM-EDS对地聚合物的矿物组成和微观形貌进行分析。结果表明:随着水淬镍渣掺量的增大,地聚合物的抗压强度先增大后降低,在镍渣掺量为50%、液固比为0.45时,地聚合物的抗压强度最大,28d达到58.8 MPa;而随着风冷镍渣掺量的增大,地聚合物的强度逐渐降低。此外,水淬镍渣/偏高岭土基地聚合物的体积变化主要表现为膨胀,而风冷镍渣/偏高岭土基地聚合物表现为收缩。