二灰水泥稳定碎石基层的力学与干缩性能

为明确二灰水泥稳定碎石在道路基层中的使用性能,采用室内实验测试不同粉煤灰掺量、不同水泥剂量下稳定碎石基层材料的无侧限抗压强度、劈裂强度、抗压回弹模量、失水率和干缩应变。结果表明:当采用二灰水泥稳定碎石铺筑二级和二级以下公路基层时,结合料中石灰与粉煤灰的质量比宜取为1:3.0左右即粉煤灰的质量分数不大于75%;从经济合理的角度考虑,应将水泥的质量分数控制在2.5%以下;为避免二灰水泥稳定碎石基层产生较大的失水率和干缩量,在实际应用中必须严格控制成型初期的保湿养生条件,以防过早产生大量干缩裂缝。     

掺乳化沥青半刚性基层混合料的路用性能研究

本文介绍了在水泥稳定碎石土和水泥粉煤灰稳定碎石土两类常用半刚性基层中加入乳化沥青后的强度和收缩路用性能的变化规律。结果表明:乳化沥青使水泥稳定碎石土和水泥粉煤灰稳定碎石土的强度下降,明显降低了两种混合料的干缩系数和温缩系数,在一定掺量范围内,掺乳化沥青可以减小半刚性基层的收缩开裂,从而使强度满足规范要求。可为半刚性基层路面的防裂作为参考。     

掺乳化沥青半刚性基层混合料的强度特性研究

在半刚性基层混合料中加入乳化沥青是为了降低半刚性基层的刚度,减小其收缩开裂。论文介绍了在石灰稳定碎石（土）、水泥稳定碎石（土）和水泥粉煤灰稳定碎石（土）三大类常用半刚性基层中加入乳化沥青后的强度和收缩变化规律,结果表明,乳化沥青使水泥稳定类的强度下降,而使石灰稳定类的强度增加,明显降低了三种混合料的干缩和温缩系数,证明了在一定掺量范围内,掺乳化沥青可以减小半刚性基层的收缩开裂。     

刍议水泥碎石抗裂性的试验

本文主要从水泥碎石抗裂性和材料强度的角度出发,将聚酯纤维掺入水泥碎石材料中,研究其对混合料的干缩系数、温缩系数、劈裂强度等所产生的影响,分析各指标的变化规律,阐述其作用机理,从而进一步提高水泥碎石的抗裂性能和强度,使水泥碎石材料更广泛地用于建设工程之中。     

大掺量钢渣微粉-水泥碱激发特性

为解决钢渣微粉在水泥基复合材料中掺配比例较低的问题，采用力学性能测试、 XRD、 SEM、 FTIR等方法研究激发剂种类、掺量等对钢渣微粉-水泥胶凝材料力学强度和微观结构的影响。结果表明：碱性激发剂可提高钢渣微粉水化速度、增大复合胶凝材料抗压强度，但激发剂种类对胶凝材料激发效果具有差异性；碳酸钠与三乙醇胺复合激发后效果显著，3、 7、 28 d龄期的最佳强度与未掺加激发剂实验组的相比分别提高47%、 72%、 69%;激发剂对复合胶凝材料浆体水化产物种类没有影响；三乙醇胺具有悬浮稳定效应以及降低溶液表面张力的能力，与碳酸钠的强腐蚀效应作用在钢渣微粉水泥体系中协同强化水化反应，使复合胶凝体系中生成更多的水化产物并且相互交织成复杂密实的空间结构。     

纳米二氧化硅对丁苯共聚物/硫铝酸盐水泥复合砂浆物理力学性能的影响

为厘清纳米二氧化硅(NS)和丁苯共聚物乳液(SB)在硫铝酸盐(CSA)水泥中的协同作用，同时解决SB/CSA水泥复合砂浆凝结时间长、抗压强度低的问题，采用NS和SB对CSA水泥砂浆进行复合改性，研究改性复合砂浆物理力学性能随NS掺量的变化，并通过测定水化放热及水化产物分析NS在SB/CSA水泥复合砂浆中的作用机制。结果表明：NS可有效缩短SB/CSA水泥复合砂浆的凝结时间，提高其抗压强度，并与SB对CSA水泥砂浆抗折强度提升具有协同作用；NS最佳掺量为1.5%,此时与不加NS的纯SB改性砂浆相比，28 d抗压和抗折强度分别提高了28%、30%。同时，掺入NS会降低复合砂浆的流动度，提高表观体积密度，降低含气量和干燥收缩率，并略微降低毛细孔吸水率。NS可通过促进无水硫铝酸钙和硫酸钙反应，进一步加快SB/CSA水泥复合浆体的水化进程，提高钙矾石的含量，从而缩短凝结时间并提高力学强度。     

公路水泥稳定碎石施工分析

向具有一定级配的碎石中加入足够多的水和水泥,再将经过拌和而得的混合料压实、养生后就能得到水泥稳定碎石了。相比石灰等材料,水泥稳定碎石的抗冻性和水稳性都更胜一筹,但是,水泥稳定碎石还是会受到水分变化的影响,有干缩裂缝的情况。在公路路面施工中,对水泥稳定碎石的质量控制是很严格的,本文就影响水泥稳定碎石强度的几个主要因素进行探讨,并进一步探究、分析,对如何在施工中保证期高质量质量提出一些想法。     

浅析高速公路水泥稳定碎石基层设计及其质量控制

为提高高速公路水泥稳定碎石基层的施工质量,对水泥稳定碎石基层的施工技术进行探讨,论述施工准备、混合料的配制、水泥稳定碎石的施工等关键性问题。     

基于振动搅拌技术高寒地区基层抗冻性与抗裂性试验研究

为了改善水泥稳定碎石半刚性基层收缩性能大,混合料拌和不均匀等,并提高基层抗冻性等路用性能,采用振动搅拌技术来改善基层的性能,提高其抗裂性和抗冻性等路用性能.振动搅拌技术是一种能较好地改善混合料拌和质量的机械强化技术.本工作研究振动搅拌水泥稳定碎石混合料的抗冻性和收缩性,对两种不同的水泥稳定碎石混合料进行了冻融试验,试验结果表明室内振动搅拌水泥稳定碎石基层材料冻融循环后强度损失比非振动搅拌水泥稳定碎石混合料冻融循环后强度损失少,且振动搅拌水泥稳定碎石基层材料的BDR值比其非振动搅拌的BDR值大,效果较为明显.由此得出振动搅拌技术有助于增强基层材料的抗冻性.根据收缩性能试验的对比分析,试验研究表明振动搅拌能很显著降低混合料的收缩应变和收缩系数;电镜试验结果也证明在振动作用下水泥结合料能更好地分散在骨料周围,使混合料能更好地成为一个整体.从试验中可以看出,振动搅拌水泥稳定碎石混合料中裂缝较均匀,裂缝宽度较小,由此表明振动作用能增强基层材料的抗裂性,减少其裂缝的产生.     

钢渣细度和掺量对钢渣复合水泥力学性能的影响

为找出在钢渣复合水泥中钢渣的最佳细度和最佳掺量,从钢渣的粉磨时间、掺量、不同助磨剂的作用和水泥配比等方面研究钢渣细度及掺量对复合水泥力学性能的影响,分析各个影响因素的作用。结果表明,随着磨细钢渣粒度的减小,钢渣复合水泥的抗折、抗压强度会有不同程度的提高;磨细钢渣的掺量为10%和20%时,钢渣复合水泥的力学性能较好,抗折、抗压强度甚至超过纯水泥;当掺量为30%和40%时,复合水泥力学强度下降幅度较大,3 d抗折强度不符合国家标准规定。     

Characterizing cement paste containing SRA modified nanoSiO2 and evaluating its strength development and shrinkage behavior

In this study, shrinkage reducing admixture (SRA) was grafted on NanoSiO₂ (NS) surfaces to synthesize novel core-shell (NS@SRA) particles and improve dispersion of NS in cement paste. The synthesized NS@SRA was characterized by Fourier transform infrared spectroscopy, dynamic light scattering, and thermogravimetric analysis. A series of tests were performed to investigate the effects of NS@SRA addition on the compressive strength and shrinkage of cement paste. It is found that NS@SRA increases the strength of cement paste, especially at later ages. Unlike conventional NS, which significantly increases autogenous shrinkage of cement paste, addition of NS@SRA does not appreciably affect autogenous shrinkage of the paste at early ages. Based on dispersion and zeta potential measurements of NS and NS@SRA particles in synthetic pore solution, we propose that hydration products around NS@SRA may result in gradual separation of SRA from the core. The released SRA may reduce shrinkage and mitigate cracking of cement composites at later ages.     

Impact of the implementation of continuous construction method on pavement cracking performance

A continuous construction method (CCM) was proposed to decrease the reflective cracking generated from the cement-treated macadam base by reducing the shrinkage of base materials and improving the bond strength at the interface between the base layer and surface layer. Traditional 3–7 days of curing period of cement-treated macadam base was eliminated by CCM and the asphalt mixture can be paved immediately after the construction of cement-treated macadam base. An anti-cracking agent was developed and added into the cement-treated base materials to prolong the hydration process and improve the shrinkage performance of base materials. The influences of anti-cracking agent on the properties of cement-treated materials were analysed using laboratory tests. The generation of micro-expansion ettringite from cement system was investigated from the microscopic perspective using the scanning electronic microscope test. Test roads were constructed and contrasted to demonstrate the feasibility of this approach and showed a superior anti-cracking performance.     

循环流化床固硫灰渣低收缩水泥的制备及性能

通过分别使用循环流化床(CFBC)固硫灰、渣代替部分原材料制备低收缩水泥熟料,加入质量分数为10%的石膏即得到CFBC固硫灰、渣低收缩水泥,然后利用X射线衍射、扫描电镜等方法研究水与水泥的质量比(简称水灰比)对CFBC固硫灰渣低收缩水泥水化程度、抗压强度和线性膨胀率的影响。结果表明,随着水灰比的增加,CFBC固硫灰渣低收缩水泥的主要水化产物钙矾石数量增多,未水化的硅酸二钙含量减少,水化程度增大;而该水泥线性膨胀率与水灰比呈正比关系,抗压强度与其呈反比关系;利用固硫灰制备的水泥早期膨胀率随着水化时间而增大,但后期由于石膏量的不足,膨胀率则随着水化时间而减小。     

The long-term creep and shrinkage behaviors of green concrete designed for bridge girder using a densified mixture design algorithm

Creep and shrinkage behaviors are critical factors in the precast/prestressed concrete industry because these factors allow engineers to assess the long-term performance of concrete and to develop life-cycle estimates for concrete structures. The current study presents the results of an experimental work that addresses creep and shrinkage behaviors as well as the development of compressive strength in ordinary Portland cement concrete (OPC), high-performance concrete (HPC), and self-consolidating concrete (SCC). The concrete mixtures created for the present study were used to fabricate prestressed bridge girders. A conventional method (ACI) was used to design the mixture proportion for OPC and a densified mixture design algorithm (DMDA) was used to design the mixture proportions for HPC and SCC. All concrete mixtures had the same target strength of 69 MPa (10000 psi) at 56 days. Additionally, a comparative performance in terms of strength development and creep and shrinkage behaviors of ACI and DMDA concrete is performed in the present study. Test results show that all of the samples attained the target strength after 28 days of curing and that the strengths of each continued to increase afterward. Importantly, the incorporation of pozzolanic materials into concrete mixtures affected the propagation of creep strain and shrinkage positively. Furthermore, the DMDA concrete sample delivered better long-term performance than ACI concrete in terms of compressive strength, creep strain, and shrinkage.     

A study on the effect of nano silica on compressive strength of high volume fly ash mortars and concretes

This paper presents the effect of nano silica (NS) on the compressive strength of mortars and concretes containing different high volume fly ash (HVFA) contents ranging from 40% to 70% (by weight) as partial replacement of cement. The compressive strength of mortars is measured at 7 and 28 days and that for concretes is measured at 3, 7, 28, 56 and 90 days. The effects of NS in microstructure development and pozzolanic reaction of pastes containing above HVFA contents are also studied through backscattered electron (BSE) image and X-ray diffraction (XRD) analysis. Results show that among different NS contents ranging from 1% to 6%, cement mortar containing 2% NS exhibited highest 7 and 28 days compressive strength. This NS content (2%) is then added to the HVFA mortars and concretes and the results show that the addition of 2% NS improved the early age (7 days) compressive strength of mortars containing 40% and 50% fly ash by 5% and 7%, respectively. However, this improvement is not observed at high fly ash contents beyond 50%. On the other hand, all HVFA mortars exhibited improvement in 28 days compressive strength due to addition of 2% NS and the most significant improvement is noticed in mortars containing more than 50% fly ash. In HVFA concretes, the improvement of early age (3 days) compressive strength is also noticed due to addition of 2% NS. The BSE and XRD analysis results also support the above findings.     

超细矿渣粉对硅酸盐水泥性能和微观结构的影响

通过掺入不同量的超细矿渣粉,研究其对普通硅酸盐水泥凝结时间、标准稠度用水量以及水泥胶砂流动性和强度的影响。结果表明,水泥浆体的初凝、终凝时间在矿渣粉掺量为5%(质量分数,下同)时有所缩短,而随着超细矿渣粉掺量的增加,初凝时间都有所延长,在掺量为20%时初凝时间最长。然而终凝时间的变化不大,只有掺量为30%时稍有延长;水泥的标准稠度用水量先减少后增加,在掺量为20%时最小;随着超细矿渣粉掺量的增大,水泥胶砂的各龄期抗折强度、3d抗压强度不断提高,7d、28d抗压强度在掺量为20%时达到最大值,之后有所降低。掺入超细矿渣粉后,能通过填充以及与水泥水化产物氢氧化钙发生反应,使水泥中氢氧化钙含量明显降低,水泥微观结构更加密实。     

改性聚丙烯纤维对发泡水泥性能的影响

采用丙烯酸化学接枝法对聚丙烯纤维进行表面改性, 研究了改性聚丙烯纤维对发泡水泥塑性收缩开裂、 力学性能及泡孔结构的影响。结果表明, 改性聚丙烯纤维可改善发泡水泥的泡孔结构, 并降低其塑性收缩开裂、 细化其塑性收缩裂缝, 同时可提高其抗折、 抗压强度及弯曲韧性。纤维与水泥的质量比为0.7%时, 试样的泡孔结构明显改善, 塑性收缩开裂值下降了85.4%, 且缝宽小于1 mm的塑性收缩裂缝比例高达73.1%, 同时试样抗折及抗压强度分别增加48.8%和30.3%, 弯曲韧性显著增加。利用傅里叶变换红外光谱仪、 SEM、 光学显微镜对改性前后聚丙烯纤维表面基团及发泡水泥试样的断面微观形貌、 泡孔结构进行了分析, 探讨了改性聚丙烯纤维的作用机制。     

高岭土对混凝土强度的影响因素研究

通过胶砂试验的方法研究了高岭土矿物掺合料对水泥胶砂的影响。由试验结果得知,28天龄期时,随高岭土量的增加,水泥胶砂抗压强度和抗折强度均下降．然而高岭土的细度和煅烧与否胶砂的强度没有影响。     

不同温度处理对磷酸镁水泥性能的影响

对磷酸镁水泥在不同温度处理下的表观形貌、体积收缩率和抗压强度进行了研究,并通过XRD、SEM对各个温度阶段的物相及微观形貌进行了分析,利用TG-DSC研究了加热过程中的质量变化和所产生的热效应。结果表明,在200℃以下,磷酸镁水泥强度减小较大;在400～800℃之间,强度变化相对较小;在更高的温度下,由于烧结现象的出现,磷酸镁水泥的强度甚至有所增长;当温度达到1400℃,磷酸镁水泥的整体结构仍然保持完整,但体积则发生了较大的收缩。磷酸镁水泥具有良好的高温稳定性。     

Sulfate attack and role of silica fume in resisting strength loss

This paper presents a detailed experimental study on the sulfate attack of Portland cement mortars, and the effectiveness of silica fume in controlling the damage arising from such attack. The test solutions used to supply the sulfate ions and cations were 5% sodium sulfate solution and 5% magnesium sulfate solution. Tap water was used as the reference solution. The main variables investigated in the study were the water/cementitious materials ratio, and the level of cement replacement. Compressive strength measured on 50 mm cubes was used to assess the changes in the mechanical properties of mortar specimens exposed to sulfate attack for 510 days. X-ray diffraction and differential scanning calorimetry were used to evaluate the microstructural nature of the sulfate attack. The test results showed that the presence of silica fume had a beneficial effect on the strength loss due to sodium sulfate attack. The best resistance to sodium sulfate attack was obtained with a SF replacement of 5–10%, but even then, a strength loss of 15–20% can be expected. On the other hand, mortars with silica fume were severely damaged in the magnesium sulfate environment. Further, the compressive strength loss actually increased with increasing SF content. The test results thus showed clearly that the use of SF in concrete exposed to magnesium sulfate solution is not recommended. The test results also showed that the w/cm ratio is the most critical parameter influencing the resistance of concrete to sulfate attack. All the tests reported in the study were carried out at 20 ± 1 °C.