共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Curing techniques and curing duration have crucial effects on the strength and other mechanical properties of mortars. Proper curing can protect against moisture loss from fresh mixes. The objective of this experimental work is to examine the compressive strength of ordinary Portland cement mortars (OMs) under various curing regimes and cement fineness. Six different curing methods including water, air, water heated, oven heated, air–water, and water–air were applied to the specimens and also six groups of mortars were used. The results showed that the highest and lowest compressive strengths are attributed to the specimens of OPC mortar water cured using grounded OPC for duration of 6 h (OM–G6–wc) and OPC mortar air cured under room temperature with oven heated after demoulding of the specimens at 60 °C for duration of 20 h (OM–OH–ac), respectively. The maximum levels obtained of compressive strengths at 7, 28, and 90 days are 57.5, 70.3, and 76.0 MPa, respectively. 相似文献
3.
The cement production industry is one of the most energy and raw materials consuming one. Over the last years a great effort is performed in order to substitute clinker for less energy demanding materials. Nevertheless, construction industry needs durable materials with improved properties. Limestone is being used in blended cements widely. The most important parameter that affects all the properties of cement paste is its pore structure. In this study, four different limestone cements were produced and their pore structure was determined by means of mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) cryoporometry. The conclusion of the study was that limestone addition affects the pore structure of the cement paste by increasing linearly the size of capillary pores from 20 nm to 40 nm when the maximum amount (35%) of limestone that is allowed by EN 197-1 is used. On the other hand the threshold diameter decreases exponentially and it is evident that limestone hardened cement pastes have many pores of the same size due to the filling effect that minerals additives have. Furthermore, limestone decreases the size of gel pores which is related to higher hydration rates. Hence, the use of limestone in cement produces a material that is structurally adequate to be used in construction. 相似文献
4.
研究了矿粉、硅灰和粉煤灰3种矿物掺合料对硫铝酸盐水泥-普通硅酸盐水泥复合体系的标准稠度用水量、凝结时间、水化放热、胶砂抗折及抗压强度、砂浆干缩率、抗硫酸盐侵蚀性能和水化产物的影响。结果表明:随矿物掺合料掺量的增加,复合体系的标准稠度用水量增大,凝结时间延长;掺加矿物掺合料后水化放热峰出现时间延后,总水化放热量减少,其中掺加矿粉和硅灰的试件初期水化速率减慢程度较掺加粉煤灰试件更明显;3种矿物掺合料对复合体系强度的影响差别较大,掺加3%硅灰的试件3 d抗压强度增长较快;硅灰的掺加会使砂浆干缩率增大,矿粉、粉煤灰的掺加可以减小砂浆试件的干缩;矿物掺合料的掺加会提高胶砂试件抗硫酸盐侵蚀性能,掺粉煤灰的试件抗硫酸盐侵蚀性能最好。 相似文献
5.
六大通用水泥标准将列入2006年度国家标准修订计划,GB 175--1999标准对推动水泥工业的发展有一定的积极作用,但随着法律法规的不断完善,市场经济的逐步建立,标准的部分条款已经不适合当前的形势及科技发展要求.现笔者根据多年来企业反映及实际工作中遇到的问题,谈几点想法和建议,仅供商榷.…… 相似文献
6.
7.
橡胶集料水泥砂浆和混凝土的性能研究 总被引:10,自引:1,他引:10
废轮胎颗粒掺加到水泥砂浆和混凝土中会明显降低材料强度,大大限制其应用。针对该问题,应用多种方法来改进橡胶混凝土的力学性能,例如降低W/C、掺加硅灰、偶联剂预处理橡胶颗粒等。研究结果表明,降低W/C能够明显提高橡胶混凝土的强度,橡胶颗粒表面用PVA和硅烷偶联剂处理能够显著增加抗压强度,如果多种方法联合使用效果更好。此外,橡胶改性混凝土的强度虽然有所降低,但其韧性和抗疲劳特性却显著增加。应用SEM分析了橡胶混凝土的微观结构,结果同样证实偶联剂处理橡胶颗粒表面能够提高水泥基体与橡胶颗粒的界面粘结强度。 相似文献
8.
为研究不同矿物组成对低热硅酸盐水泥抗海水侵蚀能力的影响,阐明低热硅酸盐水泥抗海水侵蚀的机理,利用分析纯化学试剂和水泥原材料分别制备硅酸二钙单矿和水泥熟料,并将具有不同矿物组成的低热硅酸盐水泥净浆试件在人工模拟海水中浸泡28d。通过强度发展规律、物相分析和综合热分析,发现硅酸二钙和铁铝酸四钙可以稳定低热硅酸盐水泥在海水中的强度发展,并阐明了海水中复杂盐离子与水泥水化产物反应的机理,建议适当提高铝酸三钙含量以增强低热硅酸盐水泥的抗海水侵蚀能力。 相似文献
9.
10.
Xianming Shi Zhengxian Yang Yajun Liu Doug Cross 《Construction and Building Materials》2011,25(8):3245-3256
This work aims to validate the design assumptions by the California Department of Transportation in order to better define the strategies used to design concrete structures with adequate corrosion mitigation and thus a “maintenance-free” service life. To this end, various laboratory tests were conducted to investigate the compressive strength of and chloride diffusivity in mortar and concrete samples with cement partially replaced by various minerals (class F and class N fly ash, ultra-fine fly ash, silica fume, metakaolin, and ground granulated blast-furnace slag), the porosity of mineral concretes, the freeze–thaw resistance of mineral mortars in the presence of deicers, and the effect of supplementary cementitious materials on the chloride binding and chemistry of the pore solution in mortar. 相似文献
11.
12.
The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement (CSA), ordinary Portland cement (OPC), and calcium sulfate (CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength (UCS), splitting tensile strength (STS), and volume change of fiber-added expansive mixtures were determined at different time periods (i.e. the strengths on the 28th day, and the volume changes on the 1st, 7th, 14th, 21st, and 28th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to 50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and 16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion. 相似文献
13.
Due to lack of previous research on applying additives in Cold In-Place Recycling (CIR) mixes in this study, Portland cement and lime were used as additives. The Portland cement was introduced in powder form and lime was utilized as hydrated lime in powder form and lime slurry, and the effects of each additive on properties of CIR mixes has been evaluated. The results showed that both lime and Portland cement can increase Marshall stability, resilient modulus, tensile strength, resistance to moisture damage and resistance to permanent deformation of CIR mixes. Use of Portland cement and lime slurry had better results than hydrated lime but due to the difficulties in producing lime slurry in practice, the use of Portland cement is recommended. 相似文献
14.
15.
Mineralogy of plain Portland and blended cement pastes 总被引:1,自引:0,他引:1
Hanifi Binici Ismail H. Cagatay Tahir Shah Selim Kapur 《Building and Environment》2008,43(7):1318-1325
The compressive strength and microstructure of blended cement was investigated in this study. The hydration products of cements were identified by means of scanning electron microscopy (SEM) and polarising microscopy (thin section). Results indicated that the blended cement required pozzolanic activity in addition to its cementing property with the addition of 30% material. Aggregations of belite grains were observed which were surrounded by alite. Blended cement exhibited high early-term strength. However, its 3d-age strength is lower than ordinary Portland cement. On the other hand, all blended cement mortars fulfil the compressive strength requirements of TS 24. Hence, it can be said that blended cement can achieve adequate early compressive strength. A reduction in the amount of CSH gel and the porosity of the matrix in mortars were found to be responsible for the poor compressive strength of the cement paste in early the age. 相似文献
16.
A.K. Parande B. Ramesh Babu K. Pandi M.S. Karthikeyan N. Palaniswamy 《Construction and Building Materials》2011,25(1):288-297
Wastewater treatment plant consists of pipe lines and lift stations. These plants consist of concrete pipes, manholes, pump stations, interceptors and wet wells. Entire wastewater (WW) system is forced to chemical attack due to the presence of sulphate and acid available in WW. It leads to the damage in the interior wall or structure of a sewer pipe and lift station. A concrete structure when exposed to different environments, the life of the structure is drastically reduced. Main cause of the deterioration is corrosion or erosion. The defective structures are replaced periodically which leads to indirect loss in the national growth. In other words, the failure of these structures may lead to invest more on the repair and rehabilitation.In this study, the strength of the concrete in various environments has been investigated using different techniques such as compressive strength, flexural test, rapid chloride permeability, weight loss measurements, linear polarization and open circuit potential. Microbiological examinations were also analyzed. Two types of cement namely Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC) with one mix ratio were used for complete study. Concrete specimens exposed in three environments namely: normal water (NW Potable water), domestic sewage water (DSW) and textile wastewater (TWW). From the results, it is observed that PPC exposed in different media shows better performance than OPC in both mechanical and electrochemical studies. 相似文献
17.
《Construction and Building Materials》2010,24(5):631-639
The effect of various additives (Ca(OH)2, K2SO4, Na2SO4, Al2(SO4)3) was evaluated on the hydraulic character and stability of pastes of 50–75% Fluorgypsum, 15–30% Portland cement and 10–20% Blast furnace slag. Characterization included length changes, compressive strength, SEM, DTA and XRD. The combination of Na2SO4 and Al2(SO4)3 favored early strength but caused detrimental expansion and strength losses after 90 days; whereas the use of only K2SO4 was favorable for strength and dimensional stability. The type of additive had a more important effect on stability and strength than the amounts of cement and slag. XRD indicated the presence of anhydrite, gypsum, ettringite, CaCO3 and an unidentified phase, the interaction of these is proposed to explain the behavior of the cements investigated. SEM showed that cement and slag reacted forming C–S–H that enhanced the hydraulic character by engulfing the gypsum crystals. 相似文献
18.
通过比较分析了不同煅烧温度(1200、1250、1280、1300、1350、1400、1450℃)下制成的普通硅酸盐水泥熟料和不同C2S含量(40%、45%、50%、55%)的高强低钙水泥熟料,初步确定了高强低钙水泥熟料的煅烧温度范围为1300~1400℃,以及煅烧温度与熟料矿物组成之间的影响规律。 相似文献
19.