An investigation into the properties of ternary and binary cement pastes containing glass powder

The properties of binary and ternary cement pastes containing glass powder (GP) were examined. Hydration at early age was evaluated using semi-adiabatic calorimetry and at late ages using non-evaporable water content and thermogravimetric analysis. The transport characteristic was assessed by measuring electrical resistivity. The binary paste with slag showed the highest hydration activity compared to the binary pastes with GP and fly ash (FA). The results indicated that the pozzolanic behavior of the binary paste with GP was less than that of the binary pastes with slag or FA at late ages. An increase in the electrical resistivity and compressive strength of the binary paste with GP compared to other modified pastes at late ages was observed. It was shown that GP tends to increase the drying shrinkage of the pastes. Ternary pastes containing GP did not exhibit synergistic enhancements compared to the respective binary pastes.     

水泥石的干燥收缩及其与水化程度的关系

通过梯次干燥的方式测定了水泥石在干燥过程中的重量损失和收缩变化,并结合TG-DSC综合热分析研究了水泥石水化程度与干缩的关系。结果表明,水泥石水化程度随龄期延长而逐渐提高。随着水化程度增大(由0.55到0.81),水泥石100%~84%湿度范围内收缩减小,在84%~54%收缩增大,在54%~7%湿度范围内的收缩和总收缩先增大,后有减小趋势。再润湿以后,水泥石的重量损失可以回复,但一部分干缩不可逆,大部分不可逆干缩发生在84%~54%和54%~7%湿度范围内。干燥过程改变了水泥石的孔结构,使水泥石毛细孔粗化,凝胶孔塌陷减少。     

脂肪族高效减水剂对水泥水化的微观作用机理

通过运用现代测试分析方法(RD、XRD,SEM、TG-DTA)研究了脂肪族高效减水剂对水泥水化和水泥微观结构的影响.结果分析表明,脂肪族高效减水剂能够显著有效降低水泥硬化过程中的孔隙率和孔径,改善孔的结构分布,在加入SAF减水剂1d水泥初期水化速度较慢,28d以后加入脂肪族减水剂的水泥熟料的水化程度与不加脂肪族减水剂的水泥熟料的水化程度逐渐相同.28d掺加SAF减水剂的水泥石SEM显示内部结构均匀致密、大孔减少,有大量的C-S-H凝胶生成,提高了混凝土结构的强度与耐久性.     

CFBC脱硫灰对水泥浆体水化的影响

通过对掺CFBC脱硫灰硬化水泥浆体的力学性能、结合水量、Ca(OH)2含量、水化产物以及孔隙分布的研究,分析了其对水泥浆体水化的影响。结果表明,随着CFBC脱硫灰掺量的增加,硬化水泥浆体的抗压强度降低,结合水量减少,孔隙率增加,Ca(OH)2含量减少;掺CFBC脱硫灰的水泥浆体水化产物形貌以纤维状为主,纯水泥浆体的水化产物以网络状为主。     

水泥浆液结石体强度试验研究

为了分析不同浆液配合比对水泥浆液结石体强度的影响,采用正交试验法研究了不同的水泥、速凝早强剂、膨胀剂与水结石体无侧限抗压强度和塑性强度的关系,试验结果表明,水泥浆液最佳配比为1.5∶1,速凝早强剂用量占水泥重的1.2%,膨胀剂用量占水泥重的0.02%。     

A study on the hydration rate of natural zeolite blended cement pastes

Natural zeolite is a type of mineralogical material containing large quantities of reactive SiO₂ and Al₂O_3. It is widely used in the cement industry in China as a cement blending material. Like other pozzolanic materials such as silica fume and fly ash, zeolite contributes to concrete strength mainly through the pozzolanic reaction with Ca(OH)₂, Thus, the pozzolanic reactivity of this type of material in comparison with other pozzolans is of much interest. This paper presents experimental results on the compressive strength, degree of pozzolanic reaction, and porosity of zeolite modified cement pastes. These results are compared with those obtained from similar blended cement pastes prepared with silica fume and fly ash replacements. Based on the experimental results, it can be concluded that natural zeolite is a pozzolanic material, with a reactivity between that of silica fume and fly ash. Generally, in blended cement pastes with a lower water-to-cementitious materials ratio, the natural zeolite contributes more to the strength of the pastes. But in the pastes with a higher water to cementitious ratio and a lower cement replacement level it undergoes a higher degree of reaction.     

Metakaolin sand–blended-cement pastes: Rheology,hydration process and mechanical properties

In the present work, the use of three Slovak poor metakaolin sands with different metakaolin content (36.0% (MK-1), 31.5 (MK-2) and 40.0% (MK-3)) and specific surface has been deeply studied as mineral addition for Portland cement. The percentage of metakaolin sands in the blended cements was 10%, 20% and 40%.The pozzolanic tests confirm that the three metakaolin sands show a high pozzolanic activity, comparable to a commercial metakaolin and silica fume. With respect to the rheological behaviour, metakaolin sand–blended-cement pastes fit to Herchel–Bulkley model and their yield stress increases as the metakaolin content increases. MK-3 sand with the highest pozzolanic activity and highest specific surface induces the highest increase of the yield stress.From the calorimetric results it is concluded that the addition of MK-1 and MK-2 sands to Portland cement induces a delay up to 2 h of the precipitation of the main hydration products in the blended-cement pastes and decreases the maximum heat evolution rate. On the contrary, the incorporation of 40% of MK-3 sand shortens 6 h its apparition and increases significantly the maximum heat evolution rate. Additionally, the presence of the metakaolin sands reduces the heat released during the hydration process with respect to non-blended-cement pastes.The incorporation of metakaolin sand induces a decrease of the mechanical strength, being the decrease higher as the metakaolin sand content increases although they also produce a refinement in the pore structure and a decrease of the permeability.     

Compressive strength of cement stabilized pressed earth blocks

Most codes on earthwall construction have a minimum compressive strength requirement. Kevan Heathcote of the University of Technology, Sydney acknowledges that there is no suitable method for predicting compressive strength of blocks on the manufacturing process and material constituents and sets out to examine the various factors influencing the compressive strength of cement stabilized, pressed earth blocks and to formulate a method for predicting strength based on these factors. Experimental data are used to correlate the model.     

水泥浆包裹橡胶集料法配制混凝土的抗压强度

为提高橡胶混凝土的抗压强度,采用水泥浆包裹橡胶的方法配制混凝土,并进行抗压强度测试;利用SEM、EDXA和显微硬度等测试方法,对混凝土界面过渡区结构进行表征。结果表明:采用水泥浆包裹橡胶集料的方法,与基准混凝土相比较,随橡胶集料掺量的增加,混凝土7d和28d的抗压强度虽有所降低,但降低的幅度较小;橡胶集料掺量30 kg/m~3,混凝土7d和28d的抗压强度分别为普通成型混凝土的141%和136%。水泥浆包裹橡胶法配制的混凝土抗压强度高。     

Compressive strength characteristics of cement stabilized rammed earth walls

In order to minimize the environmental impacts caused by over exploitation of natural resources for the production of building material, the possibility of using cement stabilized rammed earth for load-bearing walls has been assessed. Since the vertical load carrying capacity primarily depends on the compressive strength, a comprehensive study was conducted for rammed earth walls constructed with three commonly available laterite soil types in Sri Lanka. The results indicate the possibility of using rammed earth for single storey houses which may also be extended to two storey houses. The load deformation characteristics were used to determine the suitable partial safety factors for the structural design.     

水化硫铝酸盐水泥粉体对硫铝酸盐水泥自身水化进程的影响

制备并表征了水化硫铝酸盐水泥粉体材料(HCSAP),并结合水化热、化学收缩、XRD、TG、SEM等测试研究了HCSAP对硫铝酸盐水泥自身水化进程的影响.结果表明:在大水灰比条件下,硫铝酸盐水泥完全水化后主要生成钙矾石、水铝黄长石、单硫型水化硫铝酸钙及少量氢氧化铝.在硫铝酸盐水泥中混掺10％HCSAP,该改性浆体后期水化...     

Formation of hydrates of calcium aluminates in cement pastes with different dosages of SBR powder

The formation of hydrates of calcium aluminates in cement pastes in the presence of different dosages of styrene–butadiene rubber (SBR) powder was evaluated. The content of AFt, AFm, C₄AH₁₃ and CAH₁₀ in cement pastes was determined using XRD. The results showed that SBR powder facilitates the formation of AFt and enhances its stability. The enhanced formation of AFt results from a decrease in CH formation. AFm and C₄AH₁₃ appear after 7 and 28 days and both contents are decreased by SBR powder. Most C₃A reacts with CH after the gypsum is exhausted. CAH₁₀ is present in the cement pastes with SBR powder.     

颗粒级配对水泥浆体强度和自收缩的影响

通过实验室球磨机制备出比表面积分别为280、370和670 m2/kg三种不同细度的水泥,与不同掺量矿粉配制成不同颗粒级配的复合水泥,并进行了复合水泥干粉压实体孔隙率、复合水泥浆体的抗压强度、孔隙率、自收缩和BSEM测试。结果表明:随着水泥细度的增加,压实体的孔隙率逐渐增大。细水泥对复合水泥浆体早期孔隙的细化效果显著,提高了大掺量矿渣复合水泥浆体早期强度。矿粉的掺入减小了复合水泥体系的自收缩,矿粉掺量越大,水泥浆体自收缩越小。     

The effect of curing temperature on sulphate-resistant cement hydration and strength

This paper describes the behaviour of sulphate resistant cement paste hydrated at temperatures ranging from 4 to 85 °C. A number of techniques and methods were used to study hydration: compressive strength, thermogravimetry, X-ray diffraction, mercury intrusion porosimetry, backscattered electron imaging in conjunction with energy dispersive X-ray analysis and nuclear magnetic resonance (NMR). Early age compressive strength was found to be higher in cement pastes cured at 40 and 85 °C than in the materials hydrated at 4 and 22 °C, due to the formation of larger quantities of hydrated product in the former. The MAS NMR findings showed that this higher early age strength was related to increased CSH gel polymerization rates, and a concomitantly larger average number of units in the SiO₄ chains. The formation of CSH gels with very long chains at early ages hindered the uptake of further hydration products, however. This in turn generated more porous and less cohesive structures, causing a decline in mechanical strength, as confirmed by the backscattered electron imaging and porosity results.     

含矿渣水泥水化反应产物密度与强度变化特征

在P·Ⅱ52. 5级水泥中加入一定量的矿渣,并制备成水泥石样品,养护至不同的龄期,测定水泥石密度值、强度值与养护龄期的对应值,采用了XRD检测样品水化产物进行关联分析。试验结果分析表明:未加入矿渣的水泥石样品28 d前的强度持续增加,并高于含矿渣样品;养护至90 d,未加入矿渣的水泥石样品强度相对28 d发生了倒缩,而矿渣含量30%的水泥样品强度持续增长,并超过未加入矿渣的水泥石样品;XRD测试结果表明,矿渣的加入改变了水泥石的水化产物组成,且引起了水泥石水化产物的密度的变化,28 d后含矿渣水泥水化样品的密度呈不断增长的趋势。     

Compressive strength and shrinkage of mortar containing various amounts of mineral additions

Three mineral additions largely used in cementitious materials were tested in order to follow the shrinkage behaviour for 1 year of observation when they substitute a part of cement. The tests were carried out on standardized mortars specimen where cement was replaced by 5%, 15% and 25% of limestone, 10%, 20%, 30% of natural pozzolan and 10%, 30% and 50% of slag. The substitution of cement by 10%, 20% and 30% of limestone powder, natural pozzolan and slag respectively involves an optimal improvement of compressive strength of mortar. The separate quantification of the autogeneous and drying shrinkage development shows the effective contribution of each addition on microstructure modification and of the additional hydrates production. The microstructure was improved in the presence of limestone and of a moderate rate of slag, whereas it remains normal with natural pozzolan. The replacement rate of an active addition lower than 10% led to an additional hydrates production. This overproduction which accompanies the autogeneous shrinkage is more pronounced when cement is largely replaced by limestone. The evolutions of strength and shrinkage of mortars follow the same tendency from where it is easier to find a linear relationship giving the shrinkage deformation according to the compressive strength.     

水化热抑制剂与缓凝剂对水泥单矿及水泥水化历程的影响

研究了水化热抑制剂与不同缓凝剂对水泥凝结时间、砂浆强度的影响,及水化热抑制剂与柠檬酸缓凝剂对水泥单矿(C3A、C3S、C2S)与水泥体系水化历程的影响.结果表明:水化热抑制剂与缓凝剂对水泥的凝结时间均有一定的延缓,并使砂浆强度有所提高,其中柠檬酸与水化热抑制剂使28 d抗压强度分别提高了15.4％、12.9％;水化热抑...     

化学侵蚀下水泥土的无侧限抗压强度试验

工程上广泛使用的软土地基加固方法——水泥土搅拌法,其加固体主要是形成具有一定强度和耐久性的水泥土。通过试验探讨了各种侵蚀性的离子在不同浓度、不同pH值等条件下水泥土的力学效应。分析了在环境侵蚀下水泥土的破裂行为与机理,从而为化学损伤水泥土力学模型的建立和地下工程的长期稳定性评价提供科学依据。     

The properties of concrete made with fine dune sand

This paper presents the results of a study that investigated the properties of concrete made with dune sand. Different control concrete mixtures using ordinary Portland cement (OPC) with a minimum design compressive strength of 40 N/mm² were prepared. The amount of fine aggregates constituted about 36% by weight of all the aggregates. The workability ranged from low of 16 mm to a high of 122 mm. For each control mix, other mixtures were prepared in which the fine aggregates were replaced by different percentages of dune sand ranging from 10% to 100%. The effect of dune sand on the workability, compressive strength, tensile strength, modulus of elasticity and initial surface absorption test (ISAT) was studied. Experimental results show an improvement in the workability of concrete when fine aggregates were partially replaced by dune sand. An increase in slump was measured with increase in dune sand content. However, at high dune sand contents (above 50%); the slump starts to decrease with an increase in dune sand. Generally, the strength values decrease with increase in dune sand replacement. The strength loss was not found considerable as the maximum reduction was less than 25% when fine aggregates were fully replaced by dune sand. The absorption characteristics of concrete made with OPC as measured by the (ISAT) generally increased with higher dune sand contents.