Mechanical and durability properties of concrete made with dredged marine sand

The process of depletion of sources of natural aggregates challenges the production of technically and environmentally adequate concrete. Alternative material from marine sources, especially for concrete maritime structures, could represent an acceptable solution for this problem and it might also be of great interest for port management. This research work describes the study of the mechanical and durability properties of concretes fabricated with dredged marine sand (DMS) as a fine granular corrector in partial substitution of raw sand (from 15% to up to 50% by raw sand mass) designed for harbor pavements. Three DMS samples were extracted from the Port of Barcelona. The material was stockpiled in the open air and no washing, drying or decontamination process was carried out. Mineralogical, physical and chemical properties of DMS material were determined. Eight different mixtures were produced incorporating three types of DMS material as granular corrector in partial substitution of crushed limestone raw sand. The concretes were submitted to compressive strength tests after 7 and 28 days of moist curing, as well as density, absorption, accessible pores, elastic modulus, tensile and splitting tensile strength, abrasion, capillary suction, water penetration under pressure and ultrasonic pulse velocity (UPV) tests, all of them after 28 days of moist curing. This study shows that dredged marine sand can be successfully used as a fine aggregate for concrete production. This is justified by the similar physical and mechanical properties of concrete made with DMS comparing to reference concrete. It was verified that the use of DMS in substitution of raw sand maintained or reduced the accessible pores, the sorptivity and the water penetration depth under pressure.     

Effect of used-foundry sand on the mechanical properties of concrete

Used-foundry sand is a by-product of ferrous and nonferrous metal casting industries. Foundries successfully recycle and reuse the sand many times in a foundry. When the sand can no longer be reused in the foundry, it is removed from the foundry and is termed used/spent foundry sand. In an effort to utilize used-foundry sand in large volumes, research is being carried out for its possible large-scale utilization in making concrete as partial replacement of fine aggregate.This paper presents the results of an experimental investigation carried out to evaluate the mechanical properties of concrete mixtures in which fine aggregate (regular sand) was partially replaced with used-foundry sand (UFS). Fine aggregate was replaced with three percentages (10%, 20%, and 30%) of UFS by weight. Tests were performed for the properties of fresh concrete. Compressive strength, splitting-tensile strength, flexural strength, and modulus of elasticity were determined at 28, 56, 91, and 365 days. Test results indicated a marginal increase in the strength properties of plain concrete by the inclusion of UFS as partial replacement of fine aggregate (sand) and that can be effectively used in making good quality concrete and construction materials.     

Strength and durability of concrete incorporating crushed limestone sand

In recent years, there is a growing interest in the use of crushed sand obtained from limestone quarries in some countries where river sand is not widely available. The fines content is usually high in crushed sand which can adversely affect concrete properties. The influence of fines in crushed sand on physical and mechanical properties of concrete has been widely investigated. The results proved that up to 15% of fines content in crushed sand could be used without adversely affecting concrete strength. However, little work has been done so far on the effect of fines in crushed sand on the durability of concrete. This paper examines the influence of limestone fines in crushed sand on concrete properties. Properties include strength, water, gas and chloride-ion permeability and capillary water absorption. Four different cement types were used while maintaining a constant water/cement ratio. The results show that concrete containing 15% of limestone fines as replacement of crushed sand reduces the water permeability and increases the gas and chloride-ion permeability.     

The properties of concrete made with fine dune sand

This paper presents the results of a study that investigated the properties of concrete made with dune sand. Different control concrete mixtures using ordinary Portland cement (OPC) with a minimum design compressive strength of 40 N/mm² were prepared. The amount of fine aggregates constituted about 36% by weight of all the aggregates. The workability ranged from low of 16 mm to a high of 122 mm. For each control mix, other mixtures were prepared in which the fine aggregates were replaced by different percentages of dune sand ranging from 10% to 100%. The effect of dune sand on the workability, compressive strength, tensile strength, modulus of elasticity and initial surface absorption test (ISAT) was studied. Experimental results show an improvement in the workability of concrete when fine aggregates were partially replaced by dune sand. An increase in slump was measured with increase in dune sand content. However, at high dune sand contents (above 50%); the slump starts to decrease with an increase in dune sand. Generally, the strength values decrease with increase in dune sand replacement. The strength loss was not found considerable as the maximum reduction was less than 25% when fine aggregates were fully replaced by dune sand. The absorption characteristics of concrete made with OPC as measured by the (ISAT) generally increased with higher dune sand contents.     

Bulk engineering and durability properties of washed glass sand concrete

The paper reports the results of an experimental programme aimed at examining the performance of Portland-cement concrete produced with washed glass sand (WGS), as natural sand substitute- by mass. The effects of up to 50% WGS on fresh, engineering and durability related properties have been established and its suitability for use in a range of normal-grade concrete production assessed. WGS characteristics results showed that the post-container glass waste can be crushed to provide WGS of physical properties that satisfy the current requirements set in appropriate standards for natural sand for concrete. The density and water absorption of WGS was found to be lower than natural sand. The results for fresh concrete showed a reduction in workability of concrete with increase WGS proportion beyond 20% in the mix, although slump measurements remained within the allowable margin of ±25 mm. The mixes with high proportions of WGS were found to be less cohesive. Studies of hardened concrete properties, comprising bulk engineering properties (compressive cube and cylinder strength, flexural strength, modulus of elasticity, drying shrinkage) and durability (near surface absorption, alkali silica reaction) showed similar performance for concrete produced with natural aggregates and up to 15% WGS.     

Lightweight concrete made from oil palm shell (OPS): Structural bond and durability properties

The first part of this experimental program was to determine the structural bond properties of lightweight concrete incorporating solid waste oil palm shell (OPS) as coarse aggregate and also to compare its behaviour with other types of lightweight aggregate concretes. Other properties of OPS concrete namely the split tensile strength, modulus of rupture and modulus of elasticity were also determined. The structural bond properties were determined through pull-out test. The results showed that the experimental bond strength of OPS concrete was much higher than the design bond strength as stipulated by BS 8110. In general, the properties of OPS concrete compared well with that of other structural lightweight concretes and the results obtained encourage the use of OPS as aggregates for the production of structural lightweight concrete. The second part of the experimental program investigates the durability performance of OPS concrete through water permeability and water absorption tests.     

Strength and durability effect of modified zeolite additive on concrete properties

This paper presents an investigation into the effect of a modified zeolite additive (PWC) on strength and durability behaviour of concrete. The additive, a blend of selected alkaloids and zeolite, is commercially available and effectively used in soil stabilization for road construction. However, its influence on behaviour and performance for use in concrete has not been explored. In this research, concrete samples were prepared by incorporating PWC and/or 30% fly ash in the mixes. PWC was used in proportions of 0.6%, 0.8%, and 1.0% of the weight of cement. Concretes of 0.5 water/cementitious ratio were subjected to workability, split tensile strength, compressive strength, oxygen permeability, sorptivity, and porosity tests. Hydration behaviour of the cementitious systems and the pozzolanic effect of PWC additive were studied using differential thermal analysis and thermogravimetric analysis. Results show that PWC is effective in improving concrete strength when used at optimum proportions found to be between 0.6% and 1.0%. Sorptivity property of concrete was improved with use of PWC regardless of its proportion in the mix, while permeability of concrete improved only in the presence of 30% fly ash. PWC was found to be most effective when used in the presence of fly ash.     

Strength properties and durability aspects of high strength concrete using Korean metakaolin

Metakaolin is a cementitious material used as admixture to produce high strength concrete. In Korea, the utilization of this material remained mainly limited to fireproof walls but began recently to find applications as a replacement for silica fume in the manufacture of high performance concrete.In order to evaluate and compare the mechanical properties and durability of concrete using metakaolin, the following tests were conducted on concrete specimens using various replacements of silica fume and metakaolin; mechanical tests such as compressive, tensile and flexural strength tests, durability tests like rapid chloride permeability test, immersion test in acid solution, repeated freezing and thawing test and accelerated carbonation test.Strength tests revealed that the most appropriate strength was obtained for a substitution rate of metakaolin to binder ranging between 10% and 15%. It was observed that the resistance to chloride ion penetration reduced significantly as the proportion of silica fume and metakaolin binders increased. The filler effect resulting from the fine powder of both binders was seen to ameliorate substantially the resistance to chemical attacks in comparison with ordinary concrete. Durability tests also verified that concrete using metakaolin bore most of the mechanical and durability characteristics exhibited by concrete using silica fume. The tests implemented in this study confirmed that metakaolin constitutes a promising material as a substitute for the cost prohibitive silica fume.     

海砂资源化与海砂混凝土耐久性研究进展

针对河砂资源日益枯竭的问题,结合地方海砂的实际状况,分析了海砂资源化的必要性与可行性;通过对国外海砂资源利用情况及氯盐限量、海砂淡化技术,以及海砂混凝土耐久性研究的综述,探讨了保持和提升海砂混凝土耐久性的方法,提出在硬化混凝土表面涂覆迁移型阻锈剂,可望实现海砂的合理利用和海砂混凝土耐久性的保持与提升;最后对我国海砂资源化过程中需要解决的问题提出了建议.     

机制砂与天然细砂混掺配制高性能混凝土耐久性的研究

研究了机制砂与天然细砂混掺配制的混凝土与中砂混凝土的抗压强度、抗冻性、抗渗性、抗硫酸盐侵蚀与抗碳化性能。试验结果表明:机制砂与水泥浆体界面的结合良好;机制砂中的石粉填充了混凝土中的孔隙,提高了混凝土的密实性;机制砂与天然细砂混掺配制的混凝土,其抗冻性、抗渗性、抗硫酸盐侵蚀及抗碳化性能都优于中砂混凝土。     

海砂混凝土耐久性研究现状综述

海砂是把双刃剑,为了避免其消极作用,众多学者围绕海砂混凝土的耐久性展开了大量的研究。从海砂淡化技术、淡化海砂混凝土的性能、钢筋的锈蚀机理及阻锈措施、海砂混凝土的应用4个方面对海砂混凝土的耐久性研究状况进行了综述。     

机制砂在隧道耐久性混凝土运用中的质量控制

从母岩的选料、级配控制、石粉和泥土含量控制三个方面阐述了控制机制砂质量的重要性，并提出了可将隧道混凝土机制砂的石粉含量限值放宽到10％的建议，以促进耐久性混凝土的研究。     

机制砂配制 C55 高性能混凝土耐久性研究

某高铁建设单位要求C50及以上混凝土,必须使用河砂作为细骨料配制梁片混凝土。本文通过分别用机制砂、河砂配制C55连续梁混凝土并检测其耐久性,进而探讨机制砂配制C50及以上混凝土的可行性。     

Performance of mortar and concrete made with a fine aggregate of desert sand

At this moment there is no national specification concerning the application of desert sand with very fine grain. To be able to apply desert sand to mortar and concrete in civil engineering, mortar and concrete made of Tenggeli desert sand and Maowusu sandy land sand have been tested in order to clarify their engineering characteristics. Based on the determined chemical composition and the physical characteristics of desert sand, the mechanical properties of mortar and concrete made of two types of desert sand as fine aggregate were investigated. The results of the tests indicate that desert sand can be used as a fine aggregate in mortar and concrete for general civil engineering.     

人工砂对混凝土长期耐久性能的影响

本文结合相关混凝土耐久性试验方法,选取福州地区有代表性的人工砂,系统地研究了人工砂颗粒形貌及石粉含量对混凝土早期抗裂、收缩性、渗水高度等耐久性能的影响。     

陶砂对C50混凝土耐久性能影响的研究

研究不同掺量的陶砂对C50混凝土耐久性能的影响。试验结果表明：①陶砂对C50混凝土收缩性能的影响与陶砂掺量有关。其中,陶砂改善C50强度等级混凝土收缩性能的最佳掺量为10％：②陶砂的掺入不利于C50混凝土的抗氯离子渗透性。陶砂影响混凝土收缩性能的机理分析表明,当陶砂在混凝土中释放水进行自养护作用大于其在混凝土中由于吸水过多而导致不利于混凝土收缩变形的作用时,其才能对混凝土收缩性能有改善作用。     

路面机制砂水泥混凝土的强度与耐磨性研究

研究了水灰比、细度模数、石粉含量、洛杉矶磨耗等因素对路面机制砂水泥混凝土强度与耐磨性的影响,并与河砂混凝土进行了比较.研究结果表明:机制砂混凝土的耐磨性与强度密切相关,强度越高,耐磨性越好,同等水灰比下机制砂混凝土的耐磨性优于河砂;机制砂石粉含量在20%范围对混凝土的强度与耐磨性无不利影响.随着石粉含量的增加,机制砂混凝土的强度呈先增大后降低的趋势,磨损量减小;机制砂适当大的细度模数有利于混凝土的耐磨性;耐磨性越好的机制砂配制的混凝土磨耗值越小.     

双掺海砂混凝土的性能研究

海砂混凝土中有害氯离子是阻碍其应用的主要问题,提出了采用粉煤灰和磨细矿渣2种活性矿物复掺的方法,固化海砂混凝土中有害氯离子含量,提高海砂混凝土的耐久性。研究结果表明:双掺20%粉煤灰及30%磨细矿粉制备的海砂混凝土具有良好的力学性能及耐久性能。     

海砂对混凝土耐久性能的影响研究综述

海砂混凝土是指采用海砂为骨料制备而成的混凝土。随着河砂资源的日趋减少,致使建筑用砂逐渐短缺,利用海砂来制备混凝土,可以一定程度缓解建筑用砂短缺的压力。介绍了海砂中氯离子、硫酸根离子和贝壳类等有害物质对混凝土耐久性能的影响。针对目前海砂混凝土在开发利用方面存在的问题,概述了海砂淡化、钢筋保护法和采用新型耐腐材料(FRP)3种改进措施。最后就海砂混凝土研究现状提出了3点建议,以期为未来的研究方向提供参考。