Influence of natural coarse aggregate size,mineralogy and water content on the permeability of structural concrete

This experimental work discusses the relevance of natural coarse aggregates of different geological sources in the permeability of structural concrete. Good quality granite, basalt, calcareous and marble natural coarse aggregates, obtained from different quarries, were used to produce structural concrete of strength class C30/37. Concretes were produced with constant volume proportions, workability, mixing and curing conditions using different sizes of each aggregate type. Aggregates were mixed in concrete in both dry and water saturated states. Concrete durability parameters, such as capillary water absorption and air permeability, measured at 28 days, were found to be affected by coarse aggregate size and its water content rather than aggregate mineralogy, as discussed.     

Estimates of self-compacting concrete ‘potential’ durability

The building industry is progressively trying to use self-compacting concrete (SCC) in order to improve many aspects of construction, principally reinforced concrete. However, the problem of its durability still exists, particularly in terms of physicochemical properties which are essential to avoid corrosion of rebars. The purpose of this project was to qualify the ‘potential’ durability of self-compacting concrete and reference vibrated concrete (VC) with similar compressive strength according to French recommendations. To do this, general indicators of durability (water porosity, chloride diffusion, oxygen permeability) and additional properties necessary for a better understanding (mercury porosity, water absorption by capillarity, carbonation and ammonium nitrate leaching) were examined. Various mixes of SCC and VC were therefore made with the same raw materials in identical proportions (except for the high-performance concrete). The tests conducted on the concretes studied revealed that the durability of both concretes could be regarded as equivalent. So, at the same level of compressive strength, self-compacting concrete can be considered to be as durable as vibrated concrete.     

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.     

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.     

A study of the weathering of the Bukit Timah granite Part B: Field and laboratory investigations

Field investigations consisting of surface seismic refraction and electrical resistivity surveys, drilling and downhole geophysical logging of the rock mass and of the residual soil indicate that the weathering of the Bukit Timah granite has been rapid and is primarily caused by chemical decomposition due to the tropical climate in Singapore. The granite is usually overlain by a thick layer of residual soil. Laboratory tests indicated a large reductions of the material strength, the modulus of elasticity, the rock mass quality and other mechanical properties of the weathered granite. Apart from the mechanical properties of the residual material and/or of the weathered granite rock, physical properties including density, water content, Atterberg's limits, grain size distribution, permeability, sonic velocity and electrical resistivity were also studied in order to assess the weathering grade and the weathering processes.     

Durability of lightweight concretes with lightweight fly ash aggregates

This paper presents the effects of aggregate properties such as strength, porosity, water absorption, bulk density and specific gravity on the strength and durability of lightweight fly ash aggregate concrete (LWAC). The influence of properties of four aggregates (sintered lightweight fly ash aggregates, cold-bonded lightweight fly ash aggregate and normalweight aggregate) on mechanical and durability properties of concrete is discussed. Experimental results revealed that durable high-strength air-entrained lightweight concretes could be produced using sintered or cold-bonded lightweight fly ash aggregates, having comparable performance with the normalweight concretes. The use of lightweight aggregates (LWA) instead of normalweight aggregates in concrete production decreased the strength and stiffness due to the higher porosity and lower strength of the aggregate included in the concrete. However, permeability of sintered fly ash aggregate lightweight concretes was comparable and slightly lower than normalweight concrete whereas permeability of cold-bonded fly ash lightweight concrete was greater than the others. All concretes had a durability factor greater than 85, which met the requirements by showing quite perfect resistance to freeze–thaw.     

Performance comparison of laboratory and field produced pervious concrete mixtures

Portland cement pervious concrete (PCPC) is an environmentally friendly paving material that has been increasingly used in parking lots as well as low volume and low speed pavements. Although specifications are available for the mix design and construction of pervious concrete, there still remains a need for laboratory tests to ensure the anticipated performance of laboratory designed pervious concrete. In this study, the performance of laboratory and field produced pervious concrete mixtures as well as field cores were evaluated and compared through laboratory performance tests, including air voids, permeability, compressive and split tensile strengths, as well as Cantabro and freeze–thaw durability tests. Two types of coarse aggregate, limestone and granite, with two gradings, No. 8 and No. 89 specified in ASTM C33, were used to produce the mixtures. Latex, air-entraining admixture (AEA), and high range water reducer (HRWR) were also added to improve the overall performance of pervious concrete. The results indicated that the mixtures made with limestone and latex had lower porosity and permeability, as well as higher strength and abrasion resistance than other mixtures. Even for pervious concrete, the addition of AEA could still help to improve the freeze–thaw resistance. The comparison between laboratory and field mixtures showed that a properly designed and laboratory verified pervious concrete mixture could meet the requirements of permeability, strength, and durability performance in the field.     

Comparison of properties of steel slag and crushed limestone aggregate concretes

Steel slag is produced as a by-product during the oxidation of steel pellets in an electric arc furnace. This by-product that mainly consists of calcium carbonate is broken down to smaller sizes to be used as aggregates in asphalt and concrete. They are particularly useful in areas where good-quality aggregate is scarce. This research study was conducted to evaluate the mechanical properties and durability characteristics of steel slag aggregate concrete in comparison with the crushed limestone stone aggregate concrete. The durability performance of both steel slag and crushed limestone aggregate concretes was evaluated by assessing water permeability, pulse velocity, dimensional stability and reinforcement corrosion. The results indicated that the durability characteristics of steel slag cement concretes were better than those of crushed limestone aggregate concrete. Similarly, some of the physical properties of steel slag aggregate concrete were better than those of crushed limestone aggregate concrete, though the unit weight of the former was more than that of the latter.     

Water absorption and dehydration of natural stones versus time

Physical, chemical and mechanical properties of natural stones play an important role on deciding their application area as a building stone. In this study, water absorption and dehydration time of five different types of natural stones (marble, limestone, travertine, onyx and granite) were comparatively examined. Porosity, dry unit weight, wet unit weight, water absorption ratio and chemical analyses of the rock samples were also determined. In the light of the obtained experimental results, it was found that MgO content as the chemical property, and porosity as the physical property played a major role in the water absorption capacity and dehydration time of the studied natural stones. Basing on some observations made in this study, it was also emphasized that common standards involving the determination of water absorption coefficient by the capillarity test in rocks should be re-evaluated.     

Scrap-tyre-rubber replacement for aggregate and filler in concrete

In this research the performance of concrete mixtures incorporating 5%, 7.5% and 10% of discarded tyre rubber as aggregate and cement replacements was investigated. Numerous projects have been conducted on replacement of aggregates by crumb rubbers but scarce data are found on cementitious filler addition in the literature. Hence to examine characteristics of tyre crumb-containing concrete, two sets of concrete specimens were made. In the first set, different percentages by weight of chipped rubber were replaced for coarse aggregates and in the second set scrap-tyre powder was replaced for cement. Selected standard durability and mechanical test were performed and the results were analysed. The mechanical tests included compressive strength, tensile strength, flexural strength and modulus of elasticity. The durability tests included permeability and water absorption. The results showed that with up to 5% replacement, in each set, no major changes on concrete characteristics would occur, however, with further increase in replacement ratios considerable changes were observed.     

The effect of weathering on durability and deformability properties of granitoid rocks

In this paper, the effects of weathering on durability and deformability properties for three different types of granitoid rocks were investigated. Five weathering grades ranging from fresh to completely weathered rocks were considered for each rock type. Deformability has been evaluated based on failure strain, tangent and secant modulus. For measuring these parameters, at least five uniaxial compressive strength tests with axial strain recorded were conducted on each weathering grade. To assess the weathering effect on the durability behavior of these rocks, a slake durability test was performed up to 40 cycles. The obtained results indicated that uniaxial compressive strength and elastic modulus dramatically decrease with increasing weathering grade. After moderately weathering grade, remarkable damage was observed in the structure and fabric of considered rocks. The results from slake durability tests showed that the slake durability index for each weathering grade has a certain changes trend which can be used in determination of the weathering grade and the long-term durability assessment. Moreover, the results showed that for evaluation of the long-term durability of the mentioned rock types, at least eight cycles should be considered, while two cycles were sufficient for estimation of weathering grade.     

Mix design effective parameters on γ-ray attenuation coefficient and strength of normal and heavyweight concrete

Structures in which γ-ray production instruments are located are made of heavyweight concrete. To determine roof and wall thickness of such structures, it is necessary to measure amount of radiation absorbed. The present study was designed to investigate the effects of mix design parameters such as water to cementations materials ratio, type of aggregates and cement and pozzolanic material contents on γ-ray absorption. This paper determines attenuation coefficient of normal and heavyweight concrete. Absorption of γ-ray was both measured by experimental tests and XCOM software. Results also showed that using barite aggregates increases attenuation coefficient by 30%. Comparison of the compressive strength of normal concrete made of limestone aggregates with that of heavyweight concrete made of barite aggregates showed very close compressive strengths in both types of concrete at high W/CM values. For low W/CM values, however, compressive strength of normal concrete was higher than that of heavyweight.     

骨料对MgO混凝土开裂敏感性的影响研究

从几个典型工程中分别选取了玄武岩、角闪岩和灰岩这3种人工骨料以及花岗岩天然骨料,研究了骨料的长期吸水特性及其对MgO微膨胀混凝土变形性能的影响,利用温度应力试验机比较了用不同骨料配制的MgO微膨胀混凝土的开裂敏感性.试验结果表明,180d龄期时骨料的饱和面干吸水率相比24h时有大幅增长,骨料吸水率越高,混凝土的自收缩和干缩变形越大;采用玄武岩和角闪岩骨料配制的MgO微膨胀混凝土的开裂温度较低,元素聚类分析揭示用玄武岩和角闪岩骨料配制的混凝土界面区Ca,Mg元素富集程度较为显著,更多水化产物在此区域堆积,从而增加了界面区的密实度,有助于提高混凝土的抗裂能力.     

管桩生产中石灰石集料对混凝土强度的影响

采用石质为石灰石与石质为硅质岩的两种不同粗集料拌制混凝土,经过常压养护、压蒸养护等不同的混凝土蒸汽养护工艺,测定混凝土脱模抗压强度及压蒸后抗压强度。结果表明:石质为石灰石与石质为花岗岩的两种不同粗集料在常压养护结束后,混凝土抗压强度均有较大的增长,混凝土强度增长规律基本一致;但经压蒸养护后石质为石灰石与石质为花岗岩的两种不同粗集料配制的混凝土抗压强度产生很大的差异,石质为石灰石的粗集料配制的混凝土强度增长较低,而石质为硅质岩的粗集料配制的混凝土强度有很大的提高。     

Degradation of permeability resistance of high strength concrete after combustion

To evaluate the remaining durability of concrete materials after combustion, the permeability of high strength concrete (HSC) after combustion was studied. The transport behavior of chloride ion, water and air in concrete after combustion and the effect of temperature, strength grade, and aggregation on the permeability of HSC after combustion are investigated by chloride ion permeability coefficient (D_c), water permeability coefficient (D_w) and air permeability coefficient (D_a). The experiment results show that all three permeability coefficients commendably reflect changes of permeability. The permeability coefficient increases with the evaluation temperature. After the same temperature, the permeability coefficient of HSC is lower than that of normal strength concrete (NSC). However, the degree of degradation of permeability coefficient of HSC is greater than that of NSC. The permeability resistance of HSC containing limestone is better than that of HSC containing basalt. Combining changes of compressive strength and permeability, the remaining durability of concrete materials after combustion is appropriately evaluated.     

Reusing ceramic wastes in concrete

The ceramic industry is known to generate large amounts of calcined-clay wastes each year. So far a huge part is used in landfills. Reusing these wastes in concrete could be a win–win situation. For one hand by solving the ceramic industry waste problem and at the same time leading to a more sustainable concrete industry by reducing the use of non renewable resources like cement and aggregates and avoiding environmental problems related to land filled wastes. This paper examines the feasibility of using ceramic wastes in concrete. Results show that concrete with 20% cement replacement although it has a minor strength loss possess increase durability performance. Results also show that concrete mixtures with ceramic aggregates perform better than the control concrete mixtures concerning compressive strength, capillary water absorption, oxygen permeability and chloride diffusion thus leading to more durable concrete structures.     

润扬大桥风化花岗岩工程特性与影响因素研究

由于风化会对岩石强度、刚度和耐久性产生重大影响，故在岩石工程勘察设计中需对其进行重点研究。风化是润扬大桥花岗岩类基岩岩体质量和桥基选址与设计的控制因素之一。系统的地质分析和多种测试结果表明，桥区风化壳厚度的变化很大，岩性以及地壳升降、断裂切割、卸荷作用、江水下切与入渗等地质作用是控制花岗岩风化作用及其风化岩分布的主要因素；桥区花岗岩易风化、卸荷敏感，处于化学风化的早期阶段：细密的蚀变裂隙对岩石强度起着控制作用。在此基础上讨论了风化带来的主要岩土工程问题以及桥型方案、基础选址与设计、地基参数取值以及风化因素控制等方面的工程对策。     

Experimental assessment of long-term durability of some weak rocks

Slake durability tests, point load strength tests and X-ray diffraction analyses were carried out on thirteen rock types in an attempt to correlate the durability of the rocks with their strengths and mineral compositions. A concept is proposed to describe the rock degradation characteristics from the results of slake durability test cycles. A new classification system is introduced for rock durability, which allows the prediction of the strength of a rock when it has been affected by the weathering process. The aim of the study was to predict the influence of the weathering process (simulated by wetting and drying and heating and cooling) on the durability and strength of the volcanic, metamorphic and sedimentary rocks outcropping in eastern Thailand. Field studies were carried out in an attempt to relate the heat absorption of the rocks in situ to that measured on the laboratory specimens.     

Lightweight concrete incorporating pumice based blended cement and aggregate: Mechanical and durability characteristics

This paper presents the development of lightweight volcanic pumice concrete (VPC) using pumice based ASTM Type I blended cement (PVPC) and aggregates (both coarse and fine). The performance of VPC mixtures was evaluated by conducting comprehensive series of tests on fresh and hardened properties as well as durability. Fresh and mechanical properties of VPC mixtures such as slump, air content, compressive strength, tensile strength, density, and modulus of elasticity are described. The durability characteristics were investigated by drying shrinkage, water permeability, mercury intrusion porosimetry, differential scanning calorimetry and microhardness tests. The variables in the study include: % replacement (0%, 50%, 75% and 100% by volume) of normal weight coarse gravel aggregate by coarse lightweight volcanic pumice aggregate (VPA), replacement (100% by volume) of fine aggregate (sand) by fine VPA, constant (0.45)/variable (0.37–0.64) water-to-binder ratio by mass, variable (1.3–3.7) aggregate-to-binder ratio by mass and cement types (ASTM type I cement and PVPC). The investigation suggests the production of lightweight VPCs for structural applications having satisfactory strength and durability characteristics. The use of PVPC induces the beneficial effect of reducing the drying shrinkage and water permeability of VPC mixtures. The presence of coarse/fine/both VPA is also associated with lower permeability due to the development of high quality interfacial paste-aggregate transition zone and the progressive internal curing in VPCs. Development of non-expensive and environmentally friendly VPC with acceptable strength and durability characteristics (as illustrated in this study) can be extremely helpful for the sustainable construction and rehabilitation of volcanic disaster areas around the world.     

加气混凝土湿物理性质的测定

分析建筑围护结构的热湿过程有着重要意义,而材料的物理性质是完成分析必不可少的参数。对中国常用多孔建筑材料而言,其湿物理性质并不完备。在20~25℃下,依据ISO和ASTM标准,通过平衡吸放湿实验、压力平板实验、蒸汽渗透实验、毛细吸水实验和真空饱和实验,对中国产B07级加气混凝土进行了测试,得到了包括等温吸放湿曲线、保水曲线、蒸汽渗透系数、液态水扩散系数、吸水系数、毛细饱和含湿量和真空饱和含湿量在内的所有湿物理性质。