砒砂岩对硅酸盐和硫铝酸盐水泥性能的影响

为了研究砒砂岩对硅酸盐水泥和硫铝酸盐水泥物理性能的影响,采用单因素多水平梯度实验,通过不同砒砂岩掺量的对比,测定硅酸盐水泥和硫铝酸盐水泥的凝结时间、标准稠度用水量和胶砂强度等性能。结果表明:砒砂岩对硅酸盐水泥和硫铝酸盐水泥皆有促凝作用,当砒砂岩掺量质量分数为5%时硅酸盐水泥的初凝时间会缩短30%,硫铝酸盐水泥初凝时间缩短47%,硅酸盐水泥和硫铝酸盐水泥的标准稠度用水量分别增加6.6%和21.7%;砒砂岩掺量质量分数为10%时,硅酸盐水泥的3 d和28 d的强度分别增加7.2%和6%,对其力学性能有较大影响;掺入砒砂岩后,硫铝酸盐水泥强度降低,且随掺量增加,抗压强度降幅增大。     

磷石膏基胶凝材料的制备及无机保水剂对其性能的影响

磷石膏基胶凝材料(PGC)是由原状磷石膏、矿渣、水泥和外掺3%硅灰等配制而成的绿色胶凝材料。通过标准稠度需水量、凝结时间和抗压强度等参数确定其基本配合比,并研究无机保水剂(P-1)对PGC析水率和线膨胀率的影响,借助XRD和SEM测试手段对水化产物进行分析表征。结果表明:磷石膏掺量为50%、矿渣与水泥的比值为4∶1、外掺3%硅灰时,制备出的PGC标准稠度需水量为30.8%,初、终凝时间分别为606min和872min,室温下7d抗压强度可达25.9MPa,28d抗压强度超过40MPa。P-1掺量为2%时,析水率为1.3%,较空白样(未掺P-1)降低了62.9%,28d线膨胀率为0.3137%,较空白样降低了3.3%。PGC水化产物主要为C-S-H凝胶和少量AFt。     

石灰石粉对氯氧镁水泥性能的影响

为合理利用生产石灰石集料的副产品——石灰石粉,发展绿色建筑材料,研究了不同掺量石灰石粉对氯氧镁水泥初凝时间、终凝时间、强度、耐水性及耐硫酸盐腐蚀性能的影响,并观察了掺入石灰石粉后氯氧镁水泥微观形态的变化。试验结果表明:随着石灰石粉掺量的增加,镁水泥的初、终凝时间延长,强度逐渐降低,耐水性也逐渐降低,但硫酸盐侵蚀性能较好。在微观形态上表现为:石灰石粉的加入使胶凝相更为分散,生长出大量细长的晶体;清水浸泡时生成了大量大孔隙,硫酸盐腐蚀时生成片状晶体;但掺量即使达到40%,镁水泥的强度一样可以接近普通硅酸盐水泥的2倍。将石灰石粉大量取代轻烧粉加入氯氧镁水泥中作为建筑材料使用,是大量利用石灰石粉可供选择的良好途径。     

偏高岭土掺合料对水泥胶砂强度的影响

将不同比例的偏高岭土与矿渣、粉煤灰复合掺入水泥砂浆,分析水胶比和偏高岭土掺合料对水泥胶砂强度的影响,并借助活性指数综合分析偏高岭土掺合料的诱导激活效应。研究结果表明:偏高岭土与其他矿物参合料复掺比例一定时,随水胶比增大,水泥胶砂的强度呈下降趋势。当水胶比一定时,掺量在5%～15%范围之内,偏高岭土与矿渣复掺可提高水泥的早期强度;偏高岭土、矿渣与粉煤灰复掺更有助于改善水泥3～7d的抗折和抗压强度。偏高岭土在复掺比例为40%左右,水泥胶砂的抗折强度和抗压强度活性指数达到最佳。     

偏铝酸钠激发石灰石粉的胶凝材料合成机理研究

石灰石在地球上储量丰富。为了对石灰石粉进行高效利用，本工作采用偏铝酸钠与石灰石粉制备胶凝材料，探究了偏铝酸钠掺量对其凝结时间、力学性能的影响，分析了胶凝材料的物相组成、红外吸收特性及微观结构，揭示了石灰石粉的碱激发活化机理。试验结果进一步表明，当偏铝酸钠质量掺量为15%时，浆体在71 min时初凝；掺入20%(质量分数)的偏铝酸钠时，试样3 d抗压强度可达25.3 MPa。偏铝酸钠可促进石灰石粉的缓慢溶解、重结晶，生成层状双氢氧化物Ca₄Al₂(OH)₁₂(CO₃)·5H₂O。然而当掺入过量偏铝酸钠时，Na⁺、Al(OH)₄^-、OH^-等离子无法及时与石灰石进行反应，使得所形成胶凝材料的凝结时间延长。因此，在制备碱激发石灰石粉胶凝材料时，需控制偏铝酸钠掺量在胶凝材料总量的20%以下。本研究为碳酸钙基胶凝材料的高效应用提供重要参考。     

盾构废弃泥沙再生制备高性能注浆材料的试验研究

利用盾构施工产生的废弃泥沙与水泥复合制备了一种高性能环保型注浆材料.研究了水固比、砂胶比、减水剂掺量对注浆料稠度、流动度、凝结时间、结石率、泌水率、抗压强度等性能的影响.结果表明:随着水固比增大,注浆料的初始稠度、凝结时间、流动度均增大,而结石率、抗压强度下降.随着砂胶比增大,注浆料的初始稠度、流动度均减小,而凝结时间延长.掺入聚羧酸高性能减水剂后,注浆料的工作性能显著提升.优选的配合比为:水固比0.45,砂胶比3:1,减水剂掺量2‰.相应注浆材料的技术指标为:流动度164 mm,初始稠度118 mm,凝结时间1035 min,结石率95.7％,泌水率2.4％,3 d抗压强度12.0 MPa.     

普通硅酸盐-硫铝酸盐水泥复合凝胶体系的制备及性能研究

根据设计配比,制备了普通硅酸盐-硫铝酸盐水泥复合凝胶体系。通过改变普通硅酸盐水泥和硫铝酸盐水泥的质量比、水胶比和减水剂用量等参数,采用净浆流动度、凝胶时间、结石率、抗压强度和竖向膨胀率等实验,探究了普通硅酸盐-硫铝酸盐水泥复合凝胶体系的性能影响因素。结果表明,当硫铝酸盐水泥的用量为70%(质量分数)、水胶比为0.5、减水剂用量为0.5‰(质量分数)时,复合胶凝体系的流动度最大,达320 mm,可注性好;其初凝和终凝时间分别为6和14 min,凝胶时间短;其结石率为100%,28 d竖向膨胀率约为0.14%,无需二次注浆;其28 d抗压强度为43 MPa,加固强度高。适量的硅灰和硅渣的掺杂可以提高复合胶凝体系后期的抗压强度、抗折强度和流动度,当硅灰掺量为10%(质量分数)时,复合胶凝体系3和28 d的抗压强度、抗折强度出现了峰值;当硅渣掺量为15%(质量分数)时,复合胶凝体系28 d的抗压强度和抗折强度达到最高;当硅渣掺量为10%(质量分数)时,复合胶凝体系流动度达到334 mm。     

超细矿渣微粉浆液的制备与可注性研究

采用HN增强剂和SF胶凝剂来激发超细矿渣微粉的活性,以不同水灰比(W/C)、HN增强剂掺量、SF胶凝剂掺量为主要因素进行正交试验,测出所配超细矿渣微粉浆液的粘度、凝结时间和抗压强度(7 d和14 d),再通过追加试验获得浆液的最优配比,并将该浆液进行注浆试验。结果表明:当水灰比(W/C)为1.2、HN增强剂掺量为4%和SF胶凝剂掺量为6%时,浆液粘度为47.03,抗压强度(7 d)为5.208 KPa,表明超细矿渣微粉浆液具有良好的浆液粘度和抗压强度,比普通水泥浆液更易注入到细小砂土层中。     

酸激发提高钢渣、矿渣复合粉水硬活性的研究

叙述了分别采用硫酸和醋酸对钢渣、矿渣复合渣粉进行活性激发的试验研究结果。试验发现,经酸激发后的水泥复合渣体系的标准稠度用水量增加了约16￣17 mL左右;用硫酸激发该体系时,不同的酸浓度下初凝和终凝时间均得以延长,而醋酸激发导致凝结时间变化规律较为复杂。多数情况下,经酸激发可提高体系在各龄期的强度。考察复合渣粉活性指数可知,采用0.01￣0.1 mol/L硫酸激发复合渣粉可满足S95级矿渣粉标准对该项指标的要求。综合各龄期的测试结果,将激发用酸的浓度控制在0.1 mol/L左右是合适的。     

养护条件对碱-矿渣-偏高岭土复合胶凝材料强度的影响

研究了偏高岭土对碱矿渣水泥强度的影响规律和不同养护条件下碱-矿渣-偏高岭土复合胶凝材料(M-AAS)的强度发展情况.结果表明:80%湿度和40℃温度下,掺入适量偏高岭土能提高碱矿渣水泥的强度性能,最佳掺量为20%左右;对于掺20%偏高岭土的碱-矿渣-偏高岭土复合胶凝材料,在80%湿度下,养护温度的提高有利于抗压强度的发挥,但对抗折强度的发挥不利;在80%湿度和20℃温度下,复合材料的抗折强度出现倒缩,对80%湿度养护和水中养护两种养护条件进行适当的组合,强度倒缩现象没有发生.     

Modification of steel slag powder by mineral admixture and chemical activators to utilize in cement-based materials

Modification of steel slag powder by mineral admixture and chemical activators to utilize in cement-based materials was studied in this work. The results showed that for cement pastes with steel slag alone, the normal consistency water requirement and compressive strength were decreased significantly. Both of the initial setting time and final setting time were also retarded than that of the control sample. When a compound admixture of ground granulated blast furnace slag (GGBFS) -steel slag powder added the compressive strength was evidently improved. Modification of steel slag powder by “Gypsum-type” and “Sodium-type” chemical activators were further studied. Cement paste with the modified compound admixture by 1.5 % calcium sulfate hemihydrate or sodium sulfate, its 28 days compressive strengths could reach to 75.4 and 76.2 MPa, respectively. X-ray diffraction (XRD) patterns showed that the main hydration products mainly included Ca(OH)₂ and ettringite. It indicated that proper mineral admixture and chemical activators had a positive effect regarding early hydration of steel slag powder, and enhanced forming calcium silicate hydrate(C–S–H) gel and ettringite. This work contributes to understanding of how to sustainably manage wastes and byproduct materials and has the potential to provide several important environmental and economic benefits.     

Effect of mineral additives on the setting of blended cement by the maturity method

The addition of a mineral additive to Portland cement involves an increase of the setting time allotted to the dilution effect (dilution of the most active ingredient) and to the increase in the necessary water to prepare a normal consistency paste. In this study, ordinary cement was substituted by 5, 15 and 25% of limestone powder, 10, 20 and 30% of natural pozzolan and 10, 30 and 50% of slag. The tests of penetration are carried out every 10 min in order to determine initial and final setting time. The mortar is prepared and preserved at curing temperature of 20, 40 and 60°C. The results are analyzed and quantified by using the maturity method where the effect of each addition appears more explicit. The value of the activation energy calculated at the very early age reveals the state of activity of these mineral additives and their temperature sensitivity. For replacement amounts lower than 15%, the activation energy of the three additives increases at the initial setting and beyond this content a clear difference is observed. At the final setting time, the activation energy remains constant for limestone, increases regularly for slag and increases highly for natural pozzolan with replacement amounts above than 20%.     

Grey correlation analysis between strength of slag cement and particle fractions of slag powder

The particle size distributions of slag powder were investigated by Laser Scatter equipment. The influence of particle fractions of slag powder on the compressive strength of slag cement composed of 50% slag powder and 50% Portland cement was also studied by the method of grey correlation analysis. The results indicated that the volume fraction of particles 5–10 μm had a maximum positive effect on the mortar compressive strength of slag cement at 7 d and the volume fraction of particles 10–20 μm had a maximum positive effect on the mortar compressive strength at 28 d, whereas the volume fraction of particles larger than 20 μm had a negative effect on the mortar compressive strength at 7 and 28 d.     

The effects of CaCl<Subscript>2</Subscript>-blended acrylic polymer emulsion on the properties of cement mortar

Although acrylic polymer emulsions have been reported to impart many desirable attributes to cement mortar; delayed hydration, excessive air entrapment and moisture induced loss of strength have been highlighted as constraints. This paper explores the utilization of hydrated calcium chloride blended-acrylic polymer emulsion (CP) as a mitigation measure to these aforementioned drawbacks. First, the effects of 0, 0.5, 1.0 and 1.5% of CP by mass of cement on the early-age cement paste hydration and mortar flow were investigated. Thereafter, the influence of CP on the hardened porosity, moist-cured compressive strength, initial rate of capillary water absorption and rapid chloride permeability (RCPT) were evaluated. Test results indicate that the addition of CP to pastes sped up the cement hydration process, accelerating the final setting time of pastes by approximately 0.5–1.5 h as the CP content of pastes increased. Moreover, CP slightly increased the flow of fresh mortar, the hardened porosity of mortar mixtures containing 0.5 and 1.0% CP were also comparable to those of the plain reference mortar. With the exception of the 1.5% CP blended mortar, the 14 days moist-cured compressive strength of 0.5–1.0% CP blended mortar mixtures were also comparable to that of the plain reference mixture. Relative to the reference mixture, the addition of CP to mortar reduced the initial rate of capillary water absorption of mortar, with the mixture containing 1.5% CP giving a maximum reduction of 23%. Conversely, RCPT results indicate that above 0.5% CP addition level, CP generally increased the electrical conductivity of mixtures.     

Development of an octocalcium phosphate cement

From previous studies it is known that alpha-tertiary calcium phosphate and dicalcium phosphate form a cement upon mixing with water. In this study this cement was optimized in terms of the milling of the constituents, their molar ratio, the amount of hydroxyapatite added and the water/powder ratio. The optimum Ca/P molar ratio of the cement mixture was 1.36±0.03. X-ray diffraction showed the reaction product to be octocalcium phosphate. Addition of precipitated hydroxypatite of over 3% diminished the final strength of the cement significantly. However, admixtures of only 2% of precipitated hydroxyapatite (a) kept the final compressive strength at 30±5 MPa after soaking in Ringers solution at 37°C, (b) diminished the initial setting time from 27.5 to 10 min and the final setting time from 65 to 40 min, (c) diminished the time in which the final strength was reached from 36 to less than 14 h. The tensile strength of this cement is 19±1% of its compressive strength. The optimum water/powder ratio as found in this study was 0.30 g/g.     

Influence of key cement chemical parameters on the properties of metakaolin blended cements

The use of metakaolin (MK) as a mineral admixture for cement and concrete is a well-documented practice. The properties of cement pastes and mortars containing MK have been investigated as a function of key cement chemical parameters recognized as potential activators of the MK. Rheological behavior, initial setting time and compressive strength development have been compared by varying the total sulfate content, the nature of the added calcium sulfate and the free lime content (in the form of portlandite) in the cement. The results obtained indicate that it exists a compromise for the ratio performance/consistency in term of sulfate content and nature. Concurrently, a small addition of portlandite improves the consistency of the properties investigated.     

Performance simulation and quantitative analysis of cement-based materials subjected to leaching

A 3D numerical modelling platform (MuMoCC) developed in a previous work by the authors is applied in this paper to investigate the effect of leaching of some solid phases of cement paste (portlandite and hydrated aluminates or sulfoaluminate phases) on the mechanical and diffusivity performances of cement paste and mortar. The platform is based on a multi-scale approach and uses two numerical tools. First, NIST’s CEMHYD3D code is used to simulate 3D Representative Volume Elements of cement paste and mortar. Then mechanical and diffusivity behaviour of the numerical materials are simulated using ABAQUS software. The proposed three-dimensional heterogonous model presents at least two advantages. Firstly, it is able to capture the complexity of the random microstructure of cement-based materials. Secondly, only a few parameters have to be fitted compared to the other existing models, which indicates the relevance of the model. The numerical simulations of leached cement paste and mortar performance highlight and quantify the significant effect of portlandite and hydrated aluminate and sulfoaluminate phases’ dissolution on the decrease of elastic modulus and compressive strength and on the increase of ductility and diffusivity. The numerical results show that the leaching of portlandite decreases the compressive strength of a w/c = 0.4 cement paste by a factor of 1.33. The dissolution of portlandite and hydrated aluminates or sulfoaluminate phases involves a decrease by a more important factor (1.86).The leaching of portlandite phase involves an important increase, by a factor of 31, of the effective diffusion coefficient.Using the developed multi-scale modelling and knowing the leaching kinetics values, the mechanical and diffusion performances of cement-based materials can be estimated correctly according to leaching duration.     

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.     

Mechanical properties of reactive powder concrete containing high volumes of ground granulated blast furnace slag

The mechanical properties (flexural strength, compressive strength, toughness and fracture energy) of steel microfiber reinforced reactive powder concrete (RPC) were investigated under different curing conditions (standard, autoclave and steam curing). Portland cement was replaced with ground granulated blast furnace slag (GGBFS) at 20%, 40% and 60%. Sintered bauxite, granite and quartz were used as aggregates in different series. The compressive strength of high volume GGBFS RPC was over 250 MPa after autoclaving. When an external pressure was applied during setting and hardening stages, compressive strength reached up to 400 MPa. The amount of silica fume can be decreased with increasing amount of GGBFS. SEM micrographs revealed the tobermorite after autoclave curing.     

海工磷酸镁水泥基材料的制备及性能研究

选用海砂、海水制备了海工磷酸镁水泥基材料,研究了该材料的贮存性能,早期强度特性及抗海水侵蚀性能。结果显示磷酸镁水泥有着良好的贮存性能,原材料按一定方式存放360d后,水泥强度降低不超过5%,原材料存放1000d后,水泥强度降低不超过10%;所制备的海工磷酸镁水泥基材料,2h的抗压强度均达到28MPa以上,1d抗压强度已达52MPa以上,凝结时间在25min以内;所制备的海工磷酸镁水泥胶砂抗海水侵蚀性能良好。