Thermal analysis of borogypsum and its effects on the physical properties of Portland cement

Borogypsum, which consists mainly of gypsum crystals, B₂O₃ and some impurities, is formed during the production of boric acid from colemanite, which is an important borate ore. In this study, the effect of borogypsum and calcined borogypsum on the physical properties of ordinary Portland cement (OPC) has been investigated. The calcination temperature and transformations in the structures of borogypsum and natural gypsum were determined by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. Thermal experiments were carried out between ambient temperature and 500 °C in an air atmosphere at a heating rate of 10 °C min⁻¹. After calculation of enthalpy and determination of conversion temperatures, borogypsum (5% and 7%), hemihydrate borogypsum (5%) and natural gypsum (5%) were added separately to Portland cement clinker and cements were ground in the laboratory. The final products were tested for chemical analysis, compressive strength, setting time, Le Chatelier expansion and fineness properties according to the European Standard (EN 196). The results show that increasing the borogypsum level in Portland cement from 5% to 7% caused an increase in setting time and a decrease in soundness expansion and compressive strength. The cement prepared with borogypsum (5%) was found to have similar strength properties to those obtained with natural gypsum, whereas a mixture containing 5% of hemihydrate borogypsum was found to develop 25% higher compressive strength than the OPC control mixtures at 28 days. For this reason, utilization of calcined borogypsum in cement applications is expected to give better results than untreated borogypsum. It is concluded that hemihydrate borogypsum could be used as a retarder for Portland cement as an industrial side. This would play an important role in reducing environmental pollution.     

Utilization of borogypsum as set retarder in Portland cement production

Boron ores are used in the production of various boron compounds such as boric acid, borax and boron oxide. Boric acid is produced by reacting colemanite(2CaO·3B₂O₃·5H₂O) with sulphuric acid and a large quantity of borogypsum is formed during this production. This waste causes various environmental problems when discharged directly to the environment. Portland cement is the most important material in the building industry. This material is produced by adding about 3-5% gypsum (CaSO₄·2H₂O) to clinker as a set retarder. The aim of this study was to stabilize borogypsum, and to produce cements by adding borogypsum instead of natural gypsum to clinker. Concrete using cement produced with borogypsum was tested to find the mechanical properties and the test values were compared with those of concrete from cement with natural gypsum. Compressive strength of concrete from cement produced with borogypsum was found to be higher than that of natural gypsum. Also, the setting time of cement with borogypsum was longer than that of the Portland cement.     

脱硫石膏基无砂自流平砂浆的制备与性能研究

采用脱硫建筑石膏、P·O 42.5水泥、粉煤灰、石灰石超细粉以及外加剂为原料制备脱硫石膏基无砂自流平砂浆。采用正交试验确定石膏基胶凝材料的最优配合比,研究缓凝剂和纤维素醚对石膏基无砂自流平砂浆的性能影响,并利用XRD和SEM分别分析胶凝体系的水化产物和微观形貌,通过分析结果进一步研究外加剂的作用机理。结果表明:当脱硫石膏、水泥、粉煤灰和石灰石超细粉的质量比为16:1:2:1时,石膏基胶凝材料的强度最优;缓凝剂明显延长砂浆的凝结时间,但会导致砂浆产生泌水现象;纤维素醚可以提高砂浆的保水性,纤维素醚的引气作用造成砂浆强度下降。脱硫石膏基无砂自流平砂浆的性能指标满足《石膏基自流平砂浆》(JC/T 1023—2007)的要求。     

脱硫石膏对水泥性能的影响及其品质差异分析

对不同产地脱硫石膏作缓凝剂对水泥物理性能影响进行了研究比较,并分析探讨了脱硫石膏的品质差异及其对水泥性能影响机制。试验结果表明,与天然石膏相比,脱硫石膏对水泥早期和后期强度均有不同程度提高,但水泥凝结时间有不同程度延长。不同产地脱硫石膏对水泥与外加剂相容性、保水性、流变性和干缩率等性能的影响均存在较大差异。研究还发现,亚硫酸钙含量及钙硫比低的脱硫石膏,其水泥凝结时间、干缩性、保水性和砂浆流变性等物理性能均优于或与掺天然石膏的接近;同时,脱硫石膏的结晶程度、晶体形态和石膏溶解速率对水泥凝结时间、与外加剂相容性等也均有较大影响。     

改性磷石膏球作缓凝剂对水泥性能的影响

研究了工业化生产的改性磷石膏球对水泥标准稠度用水量、凝结时间、胶砂流动度、胶砂强度及水泥与减水剂相容性的影响,并与原状磷石膏和天然石膏进行对比,结合X-射线衍射、综合热分析等微观测试,分析了改性磷石膏球对水泥水化产物相、水化程度的影响.结果表明:采用改性磷石膏球配制的水泥,其初凝、终凝时间与掺配原状磷石膏水泥相比分别缩短217 min、227 min,1d、3d强度显著高于原状磷石膏配制的水泥,28d强度高于天然石膏配制的水泥,且标准稠度用水量、胶砂流动度、与减水剂的相容性等指标优于天然石膏配制的水泥.改性磷石膏球对水泥早期水化无不良延缓作用,且能提高水泥后期水化程度.综合对比上述三种石膏对水泥性能影响的各项指标,认为改性磷石膏球可以完全替代天然石膏作水泥缓凝剂.     

粉煤灰对水泥胶砂性能影响的试验研究

通过研究粉煤灰掺量和细度、龄期等因素对水泥胶砂流动性能、强度性能和吸水性能的影响，得出粉煤灰在上述因素下对水泥胶砂性能的影响规律。结果表明：在试验范围内，随粉煤灰掺量或比表面积增加，水泥砂浆流动性增大，需水量降低，即粉煤灰具有良好的增塑效应；随着粉煤灰掺量的增加，水泥胶砂早期强度降低，后期强度增加较快．其吸水率呈减少的趋势，这有利于抗渗性的提高；粉煤灰比表面积愈大，水泥胶砂的强度愈高，吸水率也愈小。     

Curing requirements of silica fume and fly ash mortars

The curing requirements of silica fume and fly ash mortars were investigated in this study. Silica fume and fly ash mortar specimens were moist cured for periods of 0, 3, 7, 14 and 28 days. After each of the five periods, the moist curing was interrupted by oven-drying the specimens at a temperature of 110°C for 3 days. The specimens were later tested for compressive strength and absorptivity. In this study, it was also determined whether the losses in strength and impermeability of silica fume and fly ash mortars due to an interruption in curing could be regained by recuring. The test results clearly indicate that the curing requirement of silica fume mortar is less than that of plain cement mortar, while in the case of fly ash mortar it is hogher than that of plain cement mortar.     

MSWI飞灰制CSA水泥的组成优化及性能研究

以垃圾焚烧（MSWI）飞灰为主要原料,在实验室成功烧制了硫铝酸钙（CSA）水泥熟料,继而着重研究了不同种类和不同掺量的石膏对CSA水泥的抗压强度、水化性能、标准稠度用水量和凝结时间的影响;研究了细度对CSA水泥性能的影响。结果表明：无水石膏和二水石膏均促进C4A3S^-水化,提高CSA水泥的早期强度;无水石膏的最佳掺量是5％,二水石膏可根据实际情况进行调整;掺加无水石膏的CSA水泥其标准稠度用水量较对照水泥C—II低,比对照水泥C—I有所增加;掺加5％无水石膏后水泥的凝结时间与对照水泥C-II接近,当掺量增至10％后出现急凝。本试验中,CSA水泥比表面积在288—580m^2／kg范围时均表现出良好的力学性能。     

公路粉煤灰水泥的研制（一）

文中研究了熟料掺量、复合激发剂、石膏掺量、水泥颗粒粒度对公路粉煤灰水泥的影响.获得了公路粉煤灰水泥的最佳配料方案和工艺参数.与粉煤灰硅酸盐水泥性能相比,公路粉煤灰水泥早期强度略低于粉煤灰硅酸盐水泥,凝结时间较长,但其7d～28d水化龄期内的强度增长率较高,28d强度已赶上或超过粉煤灰硅酸盐水泥,胶砂流动度好.     

Studies on high-performance blended/multiblended cements and their durability characteristics

Number of blends were prepared by intergrinding clinker, gypsum, fly ash, calcined clay, microsilica and limestone in laboratory ball mill in varying percentages, and their physical properties such as fineness, consistency, setting time and compressive strength have been determined. The durability tests on selected compositions were also conducted by exposing the mortar cubes separately in 5% Na₂SO₄ and 5% NaCl solutions till the age of 90 and 180 days. The performance was observed by compressive strength development criteria after various length of exposure. Results have been discussed and found that the durability of blended cement is higher than the ordinary Portland cement.     

Influence of natural pozzolan, colemanite ore waste, bottom ash, and fly ash on the properties of Portland cement

This study has examined the effect of natural pozzolan (NP), colemanite ore waste (CW), coal fly ash (FA), and coal bottom ash (BA) on the properties of cement and concrete. The parameters studied included compressive strength, bending strength, volume expansion, and setting time. A number of cements were prepared (in the presence of fixed quantity of 10% FA, 10% BA, and 4% CW) by the replacement of Portland cement (PC) with NP in range of 5-30%. The results showed that the final setting time of cement pastes were generally accelerated when the NP replaced part of the cement. However, NP exhibited a significant retarding effect when used in combination with CW. The results also showed that the inclusion of NP at replacement levels of 5% resulted in an increase in compressive strength of the specimens compared with that of the control concrete. The replacement of PC by 10-15% of NP in the presence of fixed quantity of CW improves the bending strength of the specimens compared with control specimens after 60 days of curing age.     

高强石膏和脱硫石膏复掺制备家用装修水泥试验研究

利用高强石膏和脱硫石膏单掺及复掺制备家庭装修水泥,通过研究其掺量变化对水泥凝结时间、胶砂强度、砂浆流动度及保水率的影响,根据小磨试验和大磨工业化试生产结果,高强石膏和脱硫石膏复掺可制备具有良好的施工性能的家装水泥。     

石膏基复合胶凝材料的物理力学性能研究

在石膏基复合胶凝材料优化配合比的基础上,研究了石膏原料煅烧温度、萘系减水剂、聚羧酸减水剂、养护条件等因素对其性能的影响,借助扫描电镜SEM、X射线衍射的表征手段,分析石膏基复合胶凝材料水化过程特点、凝结硬化作用机理.结果表明:当脱硫建筑石膏、粉煤灰、水泥、熟石灰用量分别为52%、25%、20%、3%,复合激发剂适量,基准水胶比0.40时,常温自然养护条件下该复合材料28 d和56 d抗压强度分别为24.25 MPa和26.20 MPa,软化系数0.816.常温下粉煤灰水化反应条件不同于一般水泥基材料的情况,关键是控制碱性激发剂用量应适中.适宜蒸养工艺参数为70℃、24 h,还需再经适当龄期常温养护,可以显著加快CSH凝胶和AFt的生成数量.     

常温养护粉煤灰基土聚水泥的实验研究

在常温养护条件下,分别制备了钢渣基土聚水泥和掺入钢渣与石膏的粉煤基土聚水泥,讨论了钢渣和石膏掺量对粉煤灰基土聚水泥抗压强度的影响：随钢渣或石膏含量增加,粉煤灰基土聚水泥的早期强度增大,但28d强度减小,粉煤灰中钢渣或石膏含量为10％时,土聚水泥抗压强度均超过32．5MPa。     

钢渣-粉煤灰复合胶凝材料的试验研究

以钢渣、粉煤灰等固体废物,掺加少量的普通硅酸盐水泥、脱硫石膏,辅以适量化学激发剂,研制开发新型复合胶凝材料。试验表明,少量水泥能够有效地激发出钢渣-粉煤灰体系潜在的活性,单掺水泥的钢渣-粉煤灰体系最优配比为:钢渣/粉煤灰=6:4,水泥掺量为15%;对于复掺水泥和脱硫石膏的钢渣-粉煤灰体系来说,最优配比为钢渣/粉煤灰=6:4,水泥掺量为15%,脱硫石膏掺量为10%。合适的化学激发剂可以较好地提高复合胶凝材料的性能,复合胶凝材料在自然养护的条件下比标准养护条件下强度增长更快。     

掺粉煤灰水泥胶砂的正交试验研究

采用正交试验方法,研究了粉煤灰掺量、细度和Na2SO4掺量对水泥胶砂试块抗折、抗压强度影响规律。结果表明:粉煤灰掺量对水泥胶砂试块的7d抗折、抗压强度影响最显著;粉煤灰掺量和粉煤灰细度对28d抗折、抗压强度影响都比较显著;而Na2SO4掺量对7、28d抗折、抗压强度影响不大。     

Effects of supplementary cementing materials on the properties of cement and concrete

The effect of bentonite, colemanite ore waste (CW), coal fly ash (FA) and coal bottom ash (BA) on the properties of cement and concrete has been investigated through a number of tests. The properties examined include setting time, bending strength, volume expansion, compressive strength and water consistency of the mortar. The result showed that setting time of the cements was generally accelerated when bentonite replaced a part of the cement. Bentonite exhibited a significant retarding effect when used in combination with CW in Portland cement at lower replacement level and showed an accelerating effect at higher replacement level. Although the inclusion of bentonite at replacement levels of 5-10% resulted in an increase in compressive strength at early ages, it decreased the compressive strength when used in combination with other materials. The results obtained were compared with Turkish standards and, in general, were found to be acceptable.     

Use of zeolite, coal bottom ash and fly ash as replacement materials in cement production

In this research, the effects of zeolite, coal bottom ash and fly ash as Portland cement replacement materials on the properties of cement are investigated through three different combinations of tests. These materials are substituted for Portland cement in different proportions, and physical properties such as setting time, volume expansion, compressive strength and water consistency of the mortar are determined. Then, these physical properties are compared with those of PC 42.5. The results showed that replacement materials have some effects on the mechanical properties of the cement. The inclusion of zeolite up to the level of 15% resulted in an increase in compressive strength at early ages, but resulted in a decrease in compressive strength when used in combination with fly ash. Also, setting time was decreased when zeolite was substituted. The results obtained were compared with Turkish Standards (TS), and it was found that they are above the minimum requirements.     

海工水泥原料组成的优化试验研究*

根据国家标准对海工水泥原材料组成的要求,本文以粉煤灰、矿粉、硅灰为混合材与硅酸盐水泥熟料、石膏复合,通过水泥砂浆物理性能试验、抗渗性能试验、抗硫酸盐侵蚀试验和混凝土氯离子扩散系数试验,优化、确定了海工水泥合理的原材料组成范围。试验结果表明,当熟料掺量≥33%,硅灰掺量≤3%时,所制备的海工水泥的力学性能满足国家标准42.5级海工水泥的要求;以33%的熟料、7%的石膏、17%的粉煤灰、40%的矿粉和3%的硅灰制备的海工水泥具有较好的早期、后期强度和良好的耐久性能。XRD和SEM分析结果表明,与普通硅酸盐水泥相比,海工水泥水化体系中AFt含量多,可提高水泥石的致密度,减小孔隙率,使水泥硬化体具有优异的力学性能和耐久性能。     

Packing effect and pozzolanic reaction of fly ash in mortar

This research is to study the effect of particle size of fly ash on packing effect and pozzolanic reaction of mortar when 20% of fly ash is used to replace Portland cement type I. Both effects can be determined by using fly ash and insoluble material which have almost the same particle size to replace Portland cement type I. Normally, the compressive strength of fly ash mortar is contributed from hydration reaction, packing effect, and pozzolanic reaction. For mortar mixed with insoluble material, the compressive strength is due to hydration reaction and packing effect. Thus, compressive strength due to pozzolanic reaction can be determined from the difference in compressive strength between fly ash mortar and insoluble material mortar. The results show that the strength activity index of fly ash mortar depends on the median particle size of fly ash and curing ages of mortar samples. At early ages, the strength activity index of fly ash mortar due to packing effect is higher than that due to pozzolanic reaction. At the ages of 3 to 90 days, the difference in strength activity index due to packing effect of fly ashes with median particle size of 2.7 and 160 μm is almost constant about 22% of the strength of standard mortar (STD). The differences in strength activity index due to pozzolanic reaction of fly ashes with median particle size of 2.7 and 160 μm are 3%, 20%, and 27%, respectively, at the ages of 3, 28, and 90 days.