Effects of coarse and fine aggregates on long-term mechanical properties of sea sand recycled aggregate concrete

Typical effects of coarse and fine aggregates on the long-term properties of sea sand recycled aggregate concrete (SSRAC) are analyzed by a series of axial compression tests. Two different types of fine (coarse) aggregates are considered: sea sand and river sand (natural and recycled coarse aggregates). Variations in SSRAC properties at different ages are investigated. A novel test system is developed via axial compression experiments and the digital image correlation method to obtain the deformation field and crack development of concrete. Supportive results show that the compressive strength of SSRAC increase with decreasing recycled coarse aggregate replacement percentage and increasing sea sand chloride ion content. The elastic modulus of SSRAC increases with age. However, the Poisson’s ratio reduces after 2 years. Typical axial stress–strain curves of SSRAC vary with age. Generally, the effect of coarse aggregates on the axial deformation of SSRAC is clear; however, the deformation differences between coarse aggregate and cement mortar reduce by adopting sea sand. The aggregate type changes the crack characteristics and propagation of SSRAC. Finally, an analytical expression is suggested to construct the long-term stress–strain curve of SSRAC.     

沙漠砂混凝土研究现状

将沙漠砂应用于混凝土中有效解决天然砂资源短缺与混凝土用量增加之间的矛盾,满足国民经济和工程建设的可持续发展需求。通过文献调查分析,可知目前沙漠砂混凝土处于发展阶段,大多从力学性能、耐久性、构件的受弯、抗震性能等宏观角度对其进行研究。研究表明,沙漠砂混凝土具有区域性的特点,各地区沙漠砂化学成分含量不同导致抗压强度具有一定的差异性;且掺入纤维可明显改善沙漠砂混凝土抗冻、抗渗等性能,但纤维种类不同对其改善效果不同,掺钢纤维或橡胶粉改善效果最佳;沙漠砂混凝土梁与普通砂混凝土梁破坏机理相似,且其框架柱抗震性能优于普通砂混凝土框架柱。同时沙漠砂混凝土研究未形成完整体系,在实际工程的推广应用中,有待进一步研究。     

Recycled glass replacement as fine aggregate in self-compacting concrete

With increasing environmental pressure to reduce solid waste and to recycle as much as possible, the concrete industry has adopted a number of methods to achieve this goal by replacement of waste glass with concrete composition materials. Due to differences in mixture design, placement and consolidation techniques, the strength and durability of Self Compacting Concrete (SCC) may be different than those of conventional concrete. Therefore, replacement of waste glass with fine aggregate in SCC should deeply be investigated compared to conventional concretes. The aim of the present study is to investigate the effect of glass replacement with fine aggregate on the SCC properties. In present study, fine aggregate has been replaced with waste glass in six different weight ratios ranging from 0% to 50%. Fresh results indicate that the flow-ability characteristics have been increased as the waste glass incorporated to paste volume. Nevertheless, compressive, flexural and splitting strengths of concrete containing waste glass have been shown to decrease when the content of waste glass is increased. The strength reduction of concrete in different glass replacement ratios is not remarkable, thus it can be produced SCC with waste glass as fine aggregate in a standard manner.     

沙漠砂+机制砂混凝土力学性能及碳排放研究

当前,机制砂是代替天然河砂最普遍的材料,但机制砂存在级配不均匀、石粉含量过高、生产过程消耗能源和污染环境等问题。该文结合我国西部地区沙漠砂资源丰富的情况,开展了沙漠砂+机制砂混凝土(Desert sand + Machine-made sand Concrete, DMC)的力学性能试验,分析了不同沙漠砂替代率对混凝土强度和弹性模量的影响规律：DMC的强度与弹性模量随龄期逐渐增长,养护14d和28d时DMC轴心抗压强度随着沙漠砂替代率的增加呈现出先增大后减小的趋势,当沙漠砂替代率为20%时达到峰值。试验发现,DMC抗压强度受沙漠砂替代率的影响要大于弹性模量的影响。基于混凝土可压缩堆积理论,考虑沙漠砂和机制砂混合后堆积密度的变化及机制砂与沙漠砂在外观几何形状上的差异,并将混凝土二元混合料堆积模型扩展到细骨料堆积物理参数的分析中,建立了DMC抗压强度预测模型,模型精度较高。通过案例分析,在保证车站结构材料具有较好的力学性能前提下,当采用20%DMC时,由于减少了细骨料中机制砂的使用,案例的材料碳排放较低。     

谈细集料亚甲蓝与砂当量试验

分别介绍了细集料亚甲蓝与砂当量两种不同的试验方法及实验数据的不同之处,总结归纳了两种试验方法的特点,并得出一些具有指导意义的结论。     

机制砂的试验研究与工程应用

在云、贵缺乏天然砂资源的地区,采取当地石灰岩制砂,满足工程建材需要,这是在特殊条件下的做法。文章介绍南昆线某段采用机制砂的有关石料开采、制砂工艺、配合比选配以及施工应用等情况。     

废弃陶瓷再生砂配制砂浆、混凝土的研究

混凝土作为世界上用量最大的建筑结构材料,每年用量达30亿m3,其对砂、石等天然资源的大量开采和消耗已引起严重的环境问题.利用经破碎筛分的废弃陶瓷再生砂代替天然砂配制砌筑砂浆与混凝土,进行了物理力学性能分析,并与天然砂及其砂浆、混凝土性能进行了对比.试验结果表明:废弃陶瓷再生砂性能良好,完全可以替代天然砂配制建筑砂浆和混凝土,具有良好的环境与经济效益.     

Performance characteristics of lightweight aggregate concrete containing natural pozzolan

Pozzolans are materials of natural or artificial origin that are not cementitious by themselves, but form a hydraulic cement when mixed with lime hydrate due to their aluminosiliceous composition. The reaction of pozzolan with lime already existing in cement or liberated during the hydration process modifies some properties of the cements and the resulting concrete.     

Performance of high strength concrete made with copper slag as a fine aggregate

This research study was conducted to investigate the performance of high strength concrete (HSC) made with copper slag as a fine aggregate at constant workability and to study the effect of superplasticizer addition on the properties of HSC made with copper slag. Two series of concrete mixtures were prepared with different proportions of copper slag. The first series consisted of six concrete mixtures prepared with different proportions of copper slag at constant workability. The water content was adjusted in each mixture in order to achieve the same workability as that for the control mixture. Twelve concrete mixtures were prepared in the second series. Only the first mixture was prepared using superplasticizer whereas the other eleven mixtures were prepared without using superplasticizer and with different proportions of copper slag used as sand replacement. The results indicated that the water demand reduced by almost 22% at 100% copper slag replacement compared to the control mixture. The strength and durability of HSC were generally improved with the increase of copper slag content in the concrete mixture. However, the strength and durability characteristics of HSC were adversely affected by the absence of the superplasticizer from the concrete paste despite the improvement in the concrete strength with the increase of copper content. All concrete mixtures did not meet the strength and durability design requirements due to the segregation and dryness of the concrete paste. Therefore it can be concluded that the use of copper slag as sand substitution improves HSC strength and durability characteristics at same workability while superplasticizer is very important ingredient in HSC made with copper slag in order to provide good workability and better consistency for the concrete matrix.     

Pullout response of strengthened geosynthetic interacting with fine sand

This research describes results of pullout tests performed on two new systems to reinforce the fine-grained silica sand classified as SP in the Unified Soil Classification System. The first system is composed of geogrid on which transverse steel bars are tied to make a 3-D strengthened geogrid, here called Geogrid-Bar (GGB). In the second system, plastic push pins are attached to geocomposite and a strengthened geocomposite is made, here called Geocomposite-Pin (GCP). Eighteen pullout tests were conducted with the soil relative density of 80% revealed that the use of GGB and GCP systems causes the reinforcement pullout resistance to increase by about 37% and 46%, compared with normal planar geogrid and geocomposite, respectively.     

高温后沙漠砂混凝土抗压强度超声检测

考虑温度和沙漠砂替代率两个因素,对90个尺寸为100 mm×100 mm×100 mm沙漠砂混凝土立方体进行高温试验,通过对高温后试件进行抗压强度和超声检测试验,探究沙漠砂替代率和温度对抗压强度和超声波速的影响,建立高温后相对抗压强度劣化模型,得到沙漠砂混凝土高温后相对抗压强度与相对超声波速之间的关系,为沙漠砂混凝土高温后抗压强度的无损检测提供技术支撑。     

沙漠砂高强混凝土力学性能研究

通过正交试验,分析了沙漠砂替代率、粉煤灰掺量、砂率和水胶比对沙漠砂高强混凝土7、28 d抗压强度和28 d劈裂抗拉强度的影响;在正交试验基础上,通过单因素试验,进一步研究不同沙漠砂替代率对沙漠砂高强混凝土抗压强度的影响规律。研究结果表明:用沙漠砂替代中砂配制高强混凝土是可行的;综合考虑正交试验和单因素试验的研究成果,沙漠砂高强混凝土中沙漠砂的最佳替代率0~40%。     

低温对沙漠砂C25混凝土抗压强度影响

通过设计四因素四水平正交试验,在低温条件下恒温4h,分析粉煤灰掺量、沙漠砂替代率、温度和龄期不同对沙漠砂C25混凝土在低温作用下抗压强度的影响。通过重复正交试验的方差分析及极差分析得出:在-10℃～-40℃条件下,温度对沙漠砂C25混凝土抗压强度有高度显著影响,粉煤灰掺量和龄期对沙漠砂C25混凝土低温下抗压强度有显著影响,沙漠砂替代率对沙漠砂C25混凝土低温下抗压强度影响不显著。     

采用组合矿料级配设计配制C90山砂混凝土研究

根据贵州地方砂、石材料的特性,参考公路沥青混合料标准中组合矿料级配设计方法,采用复合掺合料、聚羧酸高效减水剂和控制山砂中石粉含量等因素,最终使用P·O 42.5级水泥、Ⅱ级粉煤灰、S95级矿渣粉、硅粉配制出了28 d抗压强度大于100 MPa的C90山砂混凝土,其中利用不同粒径骨料相互搭配和山砂中适量的石粉,达到了低成...     

黄河特细砂瓷砖粘结砂浆的配制及影响因素研究

以黄河特细砂为集料制备水泥基瓷砖粘结砂浆,研究胶粉和纤维素醚用量对砂浆流动度、砂浆力学性能以及抗冻性能的影响.结果表明:砂浆稠度随着胶粉用量的增加而增大,当胶粉用量为胶凝材料质量的0.7％时,砂浆的抗压、抗折强度及抗冻性能最佳;随着纤维素醚用量的增加,砂浆稠度逐渐增大,黄河特细砂瓷砖粘结砂浆的强度逐渐降低,拉伸粘结强度逐渐增大.利用黄河特细砂制备的粘结砂浆性能符合JC/T 547-2005《陶瓷墙地砖胶粘剂》标准要求.为黄河特细砂资源的有效利用提出了一条经济可行的途径.     

预处理再生骨料混凝土性能的试验研究

对再生骨料的表观密度、吸水率、压碎指标和孔隙率等基本性能进行了研究,分析了采用水泥净浆进行表面处理后的再生骨料混凝土性能的变化。试验结果表明:通过加入高效减水剂和掺入活性掺合料(如硅灰等),用再生骨料完全可以制备出28 d强度高于50MPa的混凝土;再生粗骨料预处理对混凝土的抗冻性能影响显著,因此可以通过预处理来改善粗骨料性能,从而提高混凝土的抗冻性能。     

沙漠砂EPS轻质混凝土的制备及其力学特征研究

针对目前国内外尚无对沙漠砂EPS混凝土进行相关研究的状况,在综合现有技术的基础上,经多次试验制备出不同干密度的沙漠砂EPS混凝土试件,并对其进行了单轴压缩试验,试验结果表明:(1)沙漠砂EPS混凝土的干密度与其单轴抗压强度及割线模量E50呈线性增长关系,干密度范围在500~1 100 kg/m^3试件单轴抗压强度范围在0.5~8 MPa之间,割线模量E50在60~350 MPa之间;(2)沙漠砂EPS混凝土的力学特征介于软岩硬土之间,是一种介于两者之间的中间岩土类材料。     

一例细砂卵石商品混凝土的设计与应用

本文对细砂、卵石混凝土的有关性能进行了试验研究与分析,采用低水泥用量原则,优选出最佳砂率,配制出坍落度18cm以上且坍落度损失小的细砂卵石C25~C35商品混凝土,并提出了几点细砂卵石混凝土在实际施工中的建议。     

多孔再生骨料混凝土强度及透水性能研究

多孔再生骨料混凝土是一种新型环保型材料,为满足强度及透水性能的要求,利用普通压力试验机和自制透水试验装置对试件的7 d强度及透水系数进行了测试。分别取再生骨料取代率为0、50%、100%,水灰比为0.25、0.27、0.30,目标孔隙率为0.2和0.25,分析三个因素对多孔混凝土强度及渗透性能的影响。试验表明再生骨料因具有疏松多孔的特性,多孔再生混凝土强度随取代率的增加而降低。实测孔隙率与目标孔隙率吻合,孔隙率越大,强度值越低,透水性能越好。多孔再生混凝土孔隙率与透水性具有很好的相关性。     

再生细骨料混凝土塑性收缩开裂性能试验研究

再生细骨料在实际工程中的使用为废弃混凝土提供了一条可持续化利用的道路,而由其配制的再生细骨料混凝土开裂性能直接影响了混凝土的使用寿命。该文参考ICBO标准,采用平板约束试验,重点讨论了再生细骨料替代率、水灰比、砂率对其塑性收缩开裂性能的影响,用图像处理技术对混凝土的裂缝进行分析,计算出开裂面积进行比较。结果表明:随着再生细骨料替代率的增加,再生混凝土开裂风险增大;水灰比对再生细骨料混凝土抗裂性能至关重要,过大或过小都不利于再生混凝土防裂;选择合适的砂率可以控制再生混凝土的开裂程度。