碱激发S-MK复合固化剂固化黏土早期强度试验研究

采用偏高岭土对钢渣进行成分增补,同时使用氢氧化钠激发钢渣-偏高岭土(S-MK)复合固化剂对黏土进行固化处理,并在自然条件下养护7 d,研究S-MK复合固化剂固化黏土早期强度特性和各组分材料的最优配比.结果表明:固化黏土的早期抗压强度随着偏高岭土含量的增加表现为先增加后减小,偏高岭土掺量存在临界值,固化土早期抗压强度增长趋势平缓;固化土早期强度随着NaOH浓度的增加而增加,早期强度增长趋势表现为随浓度先平稳发展而后迅速增长,最后趋于平稳;当NaOH和偏高岭土共同作用时,偏高岭土掺量的临界值,随着NaOH浓度的增大而增大,且当NaOH浓度为7％、偏高岭土掺量10％时,试件达到最大抗压强度.     

无机矿粉对碱激发碳酸盐胶凝材料性能的影响

研究了矿渣、粉煤灰和偏高岭土时碱激发碳酸盐胶凝材料的强度、抗渗性能以及凝胶时间的影响，探讨了该材料浆体的流变特性。研究表明：1)矿渣可大幅度提高该材料的强度和抗渗性能，但会显著缩短凝胶时间；偏高岭土有利于强度的提高，但时抗渗性能和凝胶时间的影响不显著；粉煤灰时这些性能的影响均不显著；2)无机矿粉复合后，可使材料28d的抗压强度达43MPa以上，抗渗压力达1.5MPa以上；3)该胶凝材料的浆体为宾汉型流体；4)该胶凝材料中掺加粉煤灰，其浆体的流动性优于掺加矿渣和偏高岭土的浆体流动性。     

硅灰对水泥净浆抗硫酸盐侵蚀性能的改善作用

将水泥净浆试件在5%Na2SO4溶液中长期浸泡,用试件强度随浸泡时间的变化和试件中物相的XRD分析,研究了硅灰对水泥净浆抗硫酸盐侵蚀性能的影响.在Na2SO4溶液侵蚀下,普通硅酸盐水泥净浆试件强度随浸泡时间先增长,然后急剧降低;外观和XRD相分析表明,其原因是由于形成了膨胀性钙矾石,造成试件开裂破坏;加入硅灰的水泥净浆试件强度损失明显减小,尤其是抗折强度没有降低,其抵抗强度下降系数还略有增加;原因是由于硅灰的稀释作用和火山灰效应减少了水泥净浆中Ca(OH)2的量,从而降低了水泥净浆试件在硫酸盐溶液侵蚀下形成的膨胀性钙矾石的量.因而,硅灰对水泥混凝土抗硫酸盐侵蚀性能有改善作用.     

添加剂对水泥性能与水化过程的影响

研究了单组分添加剂及其复合添加剂对水泥物理性能和水化特性的影响,结果表明：单组分添加剂对水泥的细度、净浆流动性、胶砂强度均有一定提高,复合添加剂的助磨、减水、增强效果均有大幅度提高,水泥80μm筛余降低45.8%,勃氏比表面积增加了14.0%,粒径为3-30μm的颗粒明显增多.水泥粉体的SEM分析表明：添加复合添加剂能显著降低粗颗粒的比例;水泥净浆流动度由135 mm提高到了190 mm;3 d、28 d强度提高了3.2MPa和7.4MPa.水泥水化样XRD分析表明：掺入复合添加剂能提高水泥的水化速率,促进水化产物的生成.     

原状磷石膏基水硬性胶凝材料的制备与性能表征

以原状磷石膏(简称磷石膏)、水泥(P.O 42.5)、矿渣、粉煤灰为原料,将水泥、矿渣、粉煤灰粉体直接加入磷石膏浆体中进行浆粉搅拌,制备出磷石膏-矿渣-水泥基(PBC)和磷石膏-矿渣-水泥-粉煤灰(PBCF)基水硬性胶凝材料的净浆硬化试样,并对PBC和PBCF净浆硬化试样的性能进行表征。结果表明:PBC试样的3 d抗压强度较低,7,28 d龄期抗压强度随水泥掺量的增加先增加后降低,水泥掺量20%(质量分数)时,试样的7,28 d龄期抗压强度达到最大值,后者为26.4 MPa;PBCF试样的7,28 d抗压强度随粉煤灰掺量的增加先增加后降低,粉煤灰掺量为15%(质量分数)时,试样的7,28 d抗压强度均达到最大值,分别为17.0,28.7 MPa;PBCF试样软化系数均≥0.88。     

矿粉对水泥和混凝土性能的影响

为了探寻矿粉细度及掺入量对水泥和混凝土性能的影响,通过试验测试方法,分析了矿粉和水泥的基本性质,研究了超细矿粉和普通矿粉的掺量对水泥基材料标准稠度、凝结时间、流动度和力学性能的影响.结果表明：普通矿粉使水泥净浆标准稠度需水量下降,而超细矿粉则增加标准稠度需水量,两种矿粉都使水泥净浆凝结时间略微延长.普通矿粉可以改善水泥净浆的流动度,超细矿粉的加入则降低了水泥净浆的流动度.普通矿粉和超细矿粉降低水泥净浆早期（7 d）抗压强度,提高后期（28 d）抗压强度,掺10％～50％的普通矿粉的水泥净浆28 d抗压强度提高2.9％～9.7％,掺入超细矿粉28 d抗压强度提高3.9％～20.1％,普通矿粉和超细矿粉的最佳掺量为10％～30％;两种矿粉替代10％～50％水泥所配制的混凝土的强度得到了明显的提高.     

玻璃粉胶凝活性研究

用对比强度法和石灰吸收试验研究了玻璃粉的胶凝活性。结果显示,掺玻璃粉胶砂7 d强度较低,但掺量在20%以下时,28 d和56 d活性指数均在80%以上。玻璃粉对56 d胶砂抗折强度有明显改善作用,随掺量增加,抗折强度增大。玻璃粉加入Ca(OH)_2饱和溶液和水泥养护溶液中,溶液pH值随龄延长不断下降,有较高的火山灰反应活性。     

高效减水剂与缓凝剂复掺对三元胶凝体系流动性和强度的影响

针对掺萘系高效减水剂(BNS)的硅酸盐水泥-铝酸盐水泥-石膏三元胶凝体系浆体流动性小、流动性经时损失大、凝结时间短等这些问题,采用了BNS与缓凝剂柠檬酸(CA)、葡萄糖酸钠(SG)复掺的方式来予以解决,同时研究了外加剂复掺对三元胶凝体系1 d、7 d、28 d强度的影响.研究结果表明:随着CA和SG掺量的增加,三元胶凝体系浆体的流动度增大、凝结时间明显延长,且SG的作用效果较CA更加显著;CA和SG均使胶砂试件早期抗压强度小幅度降低,后期强度略有增加.     

掺合料对过硫磷石膏矿渣水泥早期性能的影响

研究了矿物掺合料偏高岭土、硅灰、硫铝酸盐水泥和外加剂水玻璃对过硫磷石膏矿渣水泥凝结速率、早期强度等早期性能的影响规律,并通过XRD、SEM等对过硫磷石膏矿渣水泥的水化及结构发展进行了研究。结果表明,在过硫磷石膏矿渣水泥中掺加水玻璃和偏高岭土,能显著提高该水泥的凝结速率和早期强度,3d、7d、28d抗压强度分别达到17MPa、32MPa、46MPa。     

量化分析珍珠岩粉在水泥基材料中的火山灰效应

为了量化地分析珍珠岩粉在水泥基材料中的火山灰效应,以判定珍珠岩磨细粉用作水泥基材料的掺合料之优劣,采用以抗压强度构成为基础的火山灰效应定量指标,研究其在水泥砂浆和混凝土中随珍珠岩粉掺量、细度及养护方式、龄期和配合比的变化特征,结果表明:经蒸压处理的混凝土即使珍珠岩粉掺量达到20％～60％(质量分数)其抗压强度也可与未掺的基准样品基本一致;对混凝土强度的绝对值而言掺合料的最佳掺量为15％(质量分数),此时混凝土强度最高;其它火山灰效应参数如R_aR_pC_p在所讨论范围内大体随着掺量增加而提高,由此研判珍珠岩磨细粉可作为水泥基材料中替代水泥的辅助胶凝材料;同时反映一种掺合料在不同的水泥基材料或养护环境中火山灰效应的差异性,为选择使用掺合料提供最佳参数依据。     

Dominant factors on the early hydration of metakaolin-cement paste

The dominant factors during early hydration process of cement paste containing 10% metakaolin replacement (MK10) and 10% kaolin replacement (K10) are investigated in comparison to neat cement paste (NCP), and X-ray Diffraction (XRD) analysis is employed to identify the crystalline phases of all specimens. Thermogravimetric (TG) and Differential Scanning Calorimetry (DSC) are used to identify the phase constituents. The amount of acid-insoluble residue (AIR) of all specimens is used to evaluate the unreacted materials. The results indicate that, after the first day, MK act as nuclei for the formation of C-S-H during hydration of C₃S and C₂S, densifying the microstructure of cement paste. Its contribution is mainly due to the fine nature of the MK. From 3 days to 7 days, more and more MK reacts with CH to form C-S-H, making the microstructure denser. The strength contribution is mainly due to the chemical activity of MK.     

Magnetic susceptibility measurements on metakaolin admixtured cement hydrated with ground water and sea water

The role of metakaolin in the properties of Portland cement hydrated with ground water and sea water was described by magnetic susceptibility study. Cement pastes containing 0wt%, 10wt%, 20wt% and 30wt% replacement of metakaolin and in a wa-ter/cement (W/C) ratio of 0.4 were prepared. The susceptibility at different hydration periods was determined by Faraday Curie bal-ance and it was related to the changes in setting time and compressive strength of admixtured cement. Compared with sea wa-ter-treated cement paste, the magnetic susceptibility of ground water-treated cement paste is higher in value. The observed result shows that, irrespective of water, the magnetic susceptibility increases with increasing metakaolin percentage replacement level in cement.     

A Comparative Study on the Pozzolanic Activity between Nano-SiO2 and Silica Fume

The pozzolanic activity of nano-SiO2 and silica fume was comparatirely stndied by X-ray diffraction （ XRD ） , differential scanning calorimetry （DSC）, scanning electron micrascopy （SEM） and the compressive , bond and bending streugths of hardened paste and concrete were also measured. Results indicate that the compressive strength development of the paste made from Ca（OH）2 and nano-SiO2, the reaction rate of Ca（ OH）2 with nano- SiO2 and the velocity of C-S-H gel formation from Ca （ OH）2 with nano-SiO2 showed marked increases over those of Ca（ OH）2 with silica fume. Furthermore, the bond strength at the interface between aggregate and hardened cement paste, and the bending strength of concrete incorporated with 3% .NS increased more than those with SF, especially at early ages. To sum up, the pozzolanic activity of nano-SiO2 was much greater than that of silica fume. The results suggest that with a small amount of nano-SiO2, the Ca（ OH）2 crystal at the interface between hardened cement paste and aggregate at early ages may be effectively absorbed in high performance concrete.     

Pore Size Distribution of High Performance Metakaolin Concrete

The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5%,10% and 20% metakaolin were prepared at a water/cementitious material ratio (W/C) of 0.30.In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison.The specimens were cured in water at 27℃ for 3 to 90 days .The results show that at the early age of curing(3 days and 7 days),metakaolin re-placements increase the compressine strength ,but silica fume replacement slightly reduces the compressine strength.At the age of and after 28 days ,the compressive strength of the concrete with metakaolin and silica fume replace-ment increases.A strong reduction in the total porosity and average pore diameter were observed in the conctete with MK 20% and 10% in the first 7 days.     

硅灰与氧化石墨烯对硬化水泥浆体的复合增强效应

研究了硅灰与氧化石墨烯复掺时对硬化水泥浆体力学性能的影响. 分别进行了普通水泥浆体、内掺质量分数10%的硅灰水泥、外掺质量分数0.8%的氧化石墨烯复合聚羧酸减水剂（GOPCs）水泥浆体以及同时内掺硅灰与外掺GOPCs的水泥浆体的配制. 对4种硬化水泥浆体的抗折强度、抗压强度以及90 d龄期孔隙率进行了测定,同时采用X射线衍射仪及扫描电子显微镜对水泥水化产物进行分析,并将4种样品的力学性能进行比较. 结果表明,当掺10%硅灰时,硬化水泥浆体90 d抗压强度比空白样提高了3.6%,抗折强度提高了9.6%;当只使用氧化石墨烯复合聚羧酸减水剂而不掺硅灰时,抗压强度提高了11.9%,抗折强度提高了15.3%;当硅灰与氧化石墨烯复掺时,抗压强度提高了22.7%,抗折强度提高了38.6%. 孔隙率的变化以及XRD、SEM分析证实了这一结果. 因此,硅灰与氧化石墨烯复合聚羧酸减水剂对硬化水泥浆体具有复合增强作用.     

再生砖骨料混凝土架构模型试验研究

通过试验研究水灰质量比、粒径级配、再生砖骨料和砂体积分数对混凝土抗压强度的影响以及灰砂质量比对水泥石抗压强度的影响,分析骨浆体积比、灰砂质量比、再生砖骨料和砂体积分数对混凝土架构贡献强度的影响. 结果表明,再生砖骨料混凝土的抗压强度随着水灰质量比的减小而增大,当骨料粒径为19~26.5 mm时抗压强度达到最大值;当再生砖骨料体积分数为30%~43.2%时,混凝土抗压强度和再生砖骨料构架贡献强度都随着再生砖骨料体积分数的增大而增大,且都随着砂体积分数的增大而增大;当灰砂质量比为0.33~1.33时,水泥砂浆试件的抗压强度随着灰砂质量比的增大而增大;当再生砖骨料体积分数为40%和43.2%时,灰砂质量比与再生砖骨料架构贡献强度以及骨浆体积比与再生砖骨料架构贡献强度均高度线性相关;再生砖骨料架构贡献强度高于混凝土强度,主要集中在再生砖骨料体积分数为40%~43.2%,特别是再生砖骨料体积分数为43.2%、砂体积分数为18%~26%.     

Characterization of pozzolanic reaction and its effect on the C-S-H Gel in fly Ash-cement paste

High resolution solid-state ²⁹Si MAS NMR, combined with XRD, SEM and FTIR were used to characterize the pozzolanic activity of FA, type of main pozzolanic reaction products, and the effect of pozzolanic reaction on the C-S-H microstructure in fly ash-cement (FC) paste. The experimental results indicate that in the hydrated FC paste with 30% dosage of FA at 3 d, FA partially participated in the pozzolanic reaction, while, at 120 d, FA largely reacts. During the hydration of FC paste at laboratory temperature, the pozzolanic reaction products are C-S-H gel rather than zeolitic gel. Moreover, after the covalent bonds of Si-O-Si, Si-O-Al and Al-O-Al in the structure of FA are broken, monosilicates Si-OH and Al-OH groups form, these chemical species can connect C-S-H dimers, thus producing more Al-free C-S-H and aluminous C-S-H than in the plain cement paste. The increased content of Al for Si substitution in the bridging tetrahedra of C-S-H may decrease the stability of C-S-H, which results in a rather obvious loss in the mechanical strength of hardened FC paste.     

偏高岭土高性能混凝土的轴压应力-应变关系

采用美国产MTS试验机,研究了掺偏高岭土(Melakaolin,MK)的混凝土轴压应力-应变关系．试验结果表明,随着MK掺量的增加,混凝土的抗压强度随之提高,特别是早期强度提高更为显著．弹性模量略有提高,但幅度明显小于强度提高值．混凝土的韧性得到改善．此外,MK对混凝土的流动性影响较小,且能显著改善粘聚性和保水性．因此,偏高岭土是一种优异的高强高性能混凝土掺合料．