Effect of prewetting methods on some fresh and hardened properties of concrete with pumice aggregate

One of the major problems in lightweight aggregate concrete production is the high water absorption characteristic of the aggregates due to their porous structure. This problem is usually overcome by prewetting the lightweight aggregates or increasing the amount of mixing water. Since aggregate prewetting methods significantly affect fresh and hardened lightweight concrete properties, it is important to take this into account before the concrete production process.This study is focused on the effects of three prewetting methods on some fresh and hardened properties of pumice lightweight concrete. Pre-soaking, water-soaking and vacuum-soaking methods were applied to pumice lightweight aggregate prior to mixing. Test results showed that fresh and hardened properties of concretes with vacuum-soaked and water-soaked lightweight aggregate were significantly better than that of concretes with pre-soaked lightweight aggregate. Vacuum-soaking and water-soaking of pumice aggregate improved workability, compressive strength and drying shrinkage of pumice lightweight concrete.     

Properties of alkali-activated mortar and concrete using lightweight aggregates

This study reports the testing of 12 alkali-activated (AA) mortars and six AA concretes using lightweight aggregates. These tests aimed to explore the significance and limitations of the development of lightweight AA mortar and concrete. Ground granulated blast-furnace slag, which was used as source material, was activated by sodium silicate powder. The main parameter investigated was the replacement level of lightweight fine aggregates to the natural sand. The effect of the water–binder ratio on the compressive strength development was also studied in AA mortars. Initial flow and development of compressive strength were recorded for the lightweight AA mortar. For the lightweight AA concrete, many factors were measured: the variation of slump with elapsed time, the development of compressive strength, splitting tensile strength, moduli of rupture and elasticity, stress–strain relationship, bond strength and shrinkage strain. Test results showed that the compressive strength of AA mortar decreased linearly with the increase of the replacement level of lightweight fine aggregates, regardless of the water–binder ratio. The compressive strength of AA concrete, however, sharply decreased when the replacement level of lightweight fine aggregates exceeded 30%. In particular, the increase in the discontinuous grading of lightweight aggregate resulted in the deterioration of the mechanical properties of AA concrete.     

Properties of concrete prepared with PVA-impregnated recycled concrete aggregates

This paper reports an experimental study to improve the properties of recycled concrete aggregates (RCA) by their impregnation with polyvinyl alcohol (PVA). The effects of PVA on the development of strength and durability properties of the recycled aggregate concrete were evaluated. The experimental investigation was conducted in two parts. Firstly, the optimal concentration of PVA solution required to improve the recycled aggregates was determined. The RCA was soaked in 6%, 8%, 10%, 12% PVA solutions, and impregnation was conducted under a controlled laboratory environment. Density, crushing value (10% fines value), and water absorption of the PVA impregnated RCA (PI-RCA) were determined. Secondly, the slump, slump loss, compressive and tensile splitting strength, dimensional change (shrinkage) and chloride penetrability of the concretes prepared with the RCA that had been impregnated with the optimal (10%) PVA concentration were determined. It was found that the 10% fines value of the PI-RCA was higher, and the water absorption of the PI-RCA were lower when compared to the untreated RCA. The results show that there was not only an improvement in the mechanical properties of the concrete made with PI-RCA, but also the shrinkage of PI-RCA decreased while the resistance to chloride-ion penetration of the concrete produced increased.     

国内节能型剪力墙技术研究和应用现状分析

节能型剪力墙体系主要由承重-保温型结构材料构成,轻骨料混凝土是应用较多的承重-保温型结构材料。本文介绍了常用的一些轻骨料混凝土的材料性能和力学性能,如抗压强度、导热系数及应力-应变本构关系等。通过对相关文献结果的比较分析得出,轻骨料混凝土剪力墙在自身热工性能上有明显改善。力学性能方面,在承载力满足设计要求的前提下,延性性能优于普通混凝土剪力墙,拥有较高的抗震安全储备。同时介绍了免拆模复合剪力墙体系和新型夹心剪力墙体系,论述了它们的热工性能和构造组成。通过对比分析,得出轻骨料混凝土是节能型剪力墙体系中具有广阔应用前景的承重-保温型材料。     

The effect of blast furnace slag on the self-compactability of pumice aggregate lightweight concrete

This paper presents the results of an experimental study of the effects of blast furnace slag, different water/(cement + mineral additive) ratios and pumice aggregates on some physical and mechanical properties of self-compacting lightweight aggregate concrete. In this study, pumice was used as lightweight aggregate. Several properties of self-compacting pumice aggregate lightweight concretes, such as unit weight, flow diameter, T50 time, flow diameter after an hour, V-funnel time, and L-box tests, 7, 28, 90 and 180-day compressive strength, 28-day splitting tensile strength, dry unit weight, water absorption, thermal conductivity and ultrasonic pulse velocity tests, were conducted. For this purpose, 18 series of concrete samples were prepared in two groups. In the first group, pumice aggregate at 100% replacement of natural aggregate was used in the production of self-compacting lightweight aggregate concrete with constant w/(c + m) ratios as 0.35, 0.40, and 0.45 by weight. Furthermore, as a second group, pumice aggregate was used as a replacement of natural aggregate, at the levels of 0, 20, 40, 60, 80, and 100% by volume. Flow diameters, T50 times, paste volumes, 28-day compressive strengths, dry unit weights, thermal conductivities and ultrasonic pulse velocity of self-compacting lightweight aggregate concrete were obtained over the range of 600–770 mm, 3–9 s, 435–540 l/m ³, 10.6–65.0 MPa, 845–2278 kg/m ³, 0.363–1.694 W/mK and 2617–4770 m/s respectively, which satisfies not only the strength requirement of semi-structural lightweight concrete but also the flowing ability requirements and thermal conductivity requirements of self-compacting lightweight aggregate concrete.     

再生粗骨料硅烷浸渍处理对混凝土介质传输性能的影响

由于残余砂浆的存在,再生粗骨料的物理力学指标远不及天然骨料,致使再生混凝土力学和耐久性能较差;此外,水分及有害离子侵入混凝土内部是引起混凝土材料性能劣化的主要原因。本试验用质量分数为8wt%的硅烷乳液浸渍强化再生粗骨料,通过抗压强度、毛细吸水和抗氯离子侵蚀试验对硅烷浸渍前后不同骨料质量取代率(0%、30%、50%)的再生混凝土介质传输性能进行了研究,最后利用SEM对再生混凝土内部的微观结构进行分析。试验结果表明,硅烷浸渍处理再生粗骨料的吸水率显著降低,由其制备的混凝土强度稍有所下降;再生混凝土毛细累积吸水量明显减少,且抗氯盐侵蚀性能显著提高,其中骨料质量取代率为50%的再生混凝土浸渍处理后氯离子扩散系数降低了37.5%。研究表明,硅烷浸渍处理再生粗骨料是提高再生混凝土耐久性的有效途径。      

Effect of polystyrene aggregate size on strength and moisture migration characteristics of lightweight concrete

The aim of this study is to investigate the effect of polystyrene aggregate size on strength and moisture migration characteristics of lightweight concrete. The present study covers the use of expanded polystyrene (EPS) and un-expanded polystyrene (UEPS) beads as lightweight aggregate in concretes that contain fly ash as a supplementary cementitious material. Lightweight concrete with wide range of concrete densities (1000–1900 kg/m³) were studied mainly for compressive strength, split tensile strength, moisture migration and absorption. The results indicate that for comparable aggregate size and concrete density, concrete with UEPS aggregate exhibited 70% higher compressive strength than EPS aggregate. EPS aggregate concrete with small EPS aggregates showed higher compressive strength and the increase in compressive strength was more pronounced in low density concrete when compared with high density concrete. The UEPS aggregate concrete exhibited brittle failure similar to normal weight concrete (NWC), whereas, gradual failure was observed in EPS concrete. Moreover, the moisture migration and absorption results indicate that the EPS concrete containing bigger size and higher volumes of EPS aggregate show higher moisture migration and absorption.     

Influence of field recycled coarse aggregate on properties of concrete

This paper investigates the influence of different amounts of recycled coarse aggregates obtained from a demolished RCC culvert 15 years old on the properties of recycled aggregate concrete (RAC). A new term called “coarse aggregate replacement ratio (CRR)” is introduced and is defined as the ratio of weight of recycled coarse aggregate to the total weight of coarse aggregate in a concrete mix. To analyze the behaviour of concrete in both the fresh and hardened state, a coarse aggregate replacement ratio of 0, 0.25, 0.50 and 1.0 are adopted in the concrete mixes. The properties namely compressive and indirect tensile strengths, modulus of elasticity, water absorption, volume of voids, density of hardened concrete and depth of chloride penetration are studied. From the experimental results it is observed that the concrete cured in air after 7 days of wet curing shows better strength than concrete cured completely under water for 28 days for all coarse aggregate replacement ratios. The volume of voids and water absorption of recycled aggregate concrete are 2.61 and 1.82% higher than those of normal concrete due to the high absorption capacity of old mortar adhered to recycled aggregates. The relationships among compressive strength, tensile strengths and modulus of elasticity are developed and verified with the models reported in the literature for both normal and recycled aggregate concrete. In addition, the non-destructive testing parameters such as rebound number and UPV (Ultrasonic pulse velocity) are reported. The study demonstrates the potential use of field recycled coarse aggregates (RCA) in concrete.     

A novel material for lightweight concrete production

This paper presents the results of an experimental study on the effects of using recycled waste expanded polystyrene foam (EPS), as a potential aggregate in lightweight concrete. In this study, thermally modified waste EPS foams have been used as aggregate. Modified waste expanded polystyrene aggregates (MEPS) were obtained by heat treatment method by keeping waste EPS foams in a hot air oven at 130 °C for 15 min. Effects of MEPS aggregate on several properties of concrete were investigated. For this purpose, six series of concrete samples were prepared. MEPS aggregate was used as a replacement of natural aggregate, at the levels of 0%, 25%, 50%, 75%, and 100% by volume. The density of MEPS is much less than that of natural aggregate; MEPS concrete becomes a lightweight concrete with a density of about 900–1700 kg/m³. The 28-d compressive strengths of MEPS concrete range from 12.58 MPa to 23.34 MPa, which satisfies the strength requirement of semi-structural lightweight concrete.     

Effects of cold-bonded fly ash aggregate properties on the shrinkage cracking of lightweight concretes

This paper presents an experimental study on the restrained shrinkage cracking of the lightweight concretes made with cold-bonded fly ash lightweight aggregates. Two types of fly ash having different physical and chemical properties were utilized in the production of lightweight aggregates with different strengths. Afterwards, lower strength aggregates were also surface treated by water glass and cement–silica fume slurry to improve physical and mechanical properties of the particles. Therefore, a total of eight concrete mixtures were designed and cast at 0.35 and 0.55 water–cement ratios using four types of lightweight coarse aggregates differing in their surface texture, density, water absorption, and strength. Ring type specimens were used for restrained shrinkage cracking test. Free shrinkage, creep, weight loss, compressive and splitting tensile strengths, and modulus of elasticity of the concretes were also investigated. Results indicated that improvement in the lightweight aggregate properties extended the cracking time of the concretes resulting in finer cracks associated with the lower free shrinkage. Moreover, there was a marked increase in the compressive and splitting tensile strengths, and the modulus of elasticity.     

Post-fire mechanical performance of concrete made with selected plastic waste aggregates

This paper presents an experimental study about the effects of elevated temperatures on the residual mechanical properties of concrete incorporating selected plastic waste aggregates (PWAs). Six different concrete mixes were prepared: a reference concrete (RC) made with natural aggregates (NAs) and five concrete mixes with replacement ratios of 7.5% and 15% of natural aggregate by three types of polyethylene terephthalate (PET) plastic waste aggregate (CPWA). Specimens were exposed to temperatures of 600 °C and 800 °C for a period of 1 h, after being heated in accordance with the ISO 834 time–temperature curve. After cooling down to ambient temperature, the following properties were evaluated and compared with reference values obtained prior to fire exposure: (i) compressive and (ii) splitting tensile strengths, (iii) elastic modulus, (iv) ultrasonic pulse velocity (UPV), (v) surface hardness, and (vi) water absorption by immersion. For the replacement ratios used in these experiments, the maximum temperatures reached in CPWA were higher than those measured in RC, due to the higher porosity increase with temperature of the former type of concrete that facilitated the propagation of heat inside concrete, and the exothermic thermal decomposition of plastic aggregates that generated additional heat. After exposure to elevated temperatures, the degradation of compressive strength and elastic modulus of CPWA was higher than that of RC, particularly for the highest replacement ratio, as a consequence of the higher porosity increase experienced by CPWA. The reduction of residual splitting tensile strength of CPWA was found to be similar to that of RC, possibly because the incorporation of PWA led to lower internal stresses due to thermal gradients and allowed an easier dispersion of gases confined in pores, thus reducing crack development in the matrix. The magnitude of the degradation of concrete’s residual mechanical properties was seen to depend on the type of PWAs and the replacement ratio. The residual compressive strength of CPWA proved to be strongly correlated with both UPV and water absorption by immersion, but its correlation with surface hardness was less significant.     

New production process for insulation blocks composed of EPS and lightweight concrete containing pumice aggregate

This study introduces a new production method for production of the insulation blocks made of pumice aggregate, lightweight concrete and expanded polystyrene foam (EPS). Products produced via this method were analyzed for compliance with the Turkish standards institution (TS EN) standards. A single-line lightweight masonry block with 200?mm?×?400?mm?×?200?mm dimension (width?×?length?×?height) was produced to produce an insulation block by using circular saw block cutting machine for the first time. Physical and thermal properties of the all-in aggregate pumice used in lightweight aggregate were determined and the all-in aggregate pumice was subjected to sieve analysis. After the production, insulation blocks were subjected to some analysis according to pre-set standards to determine their usability as masonry unit. After the curing period (28?days), it was found that the highest value of deviation from the plane was 0.150?mm; deviation of the flanges from plain parallelism was 0.40?mm; dry density was 562?kg/m³; compressive strength value was 2.99?N/mm²; water absorption coefficient by capillaries was 20.63?g/mm²sn^0.5; sound absorption value of the masonry unit was 60 (dB); thermal conductivity coefficient was 0.33?W/mK; initial shear strength value was 0.471?N/mm² and plaster-holding capacity was considerably high. When compared to other construction elements, thermal conductivity and masonry unit weight of the insulation block and masonry costs were found to be lower.     

Effect of aggregate properties on the strength and stiffness of lightweight concrete

An experimental program was carried out to obtain the compressive strengths and elastic moduli of cold-bonded pelletized lightweight aggregate concretes. Three types of aggregates were made with different fly ash contents. Experimental data were analyzed statistically. Test results of multivariate analysis of variance (MANOVA) with 95% confidence level (α=0.05) show that the properties of lightweight aggregates and the water/binder ratio are two significant factors affecting the compressive strength and elastic modulus of concrete.     

Using aggregate flowability testing to predict lightweight self-consolidating concrete plastic properties

This paper presents the results of an experimental study on the flow properties of lightweight self-consolidating concrete (LWSCC) which utilizes a new test relating aggregate flow to concrete flow. Three types of LWSCC were tested containing differing proportions of lightweight and normal weight, coarse and fine aggregates, as well as a normal weight self-consolidating concrete (NWSCC) as a control. The flow properties of the aggregate mixes used in the LWSCC and NWSCC specimens were tested using a V-funnel. The concrete flow properties were also tested for comparison, as were the compressive and tensile strengths of the various mixtures. A relationship between the aggregate frictional resistance and the traditional concrete flowability tests—i.e., slump flow, J-ring, and T₅₀₀—was demonstrated. Compressive strengths were greater in LWSCC mixes that contained smaller sized coarse and normal weight aggregates. Finally, a design procedure is introduced that utilizes the aggregate frictional resistance, paste flow properties, and aggregate void ratio to predict the plastic properties of the concrete.     

Lightweight geopolymer concrete containing aggregate from recycle lightweight block

In this research, the properties of lightweight geopolymer concrete containing aggregate from recycle lightweight block were studied. The recycle block was crushed and classified as fine, medium and coarse aggregates. The compressive strength and density with various liquid alkaline/ash ratios, sodium silicate/NaOH ratios, NaOH concentrations, aggregate/ash ratios and curing temperatures were tested. In addition, porosity, water absorption, and modulus of elasticity were determined. Results showed that the lightweight geopolymer blocks with satisfactory strength and density could be made. The 28-day compressive strength of 1.0–16.0 MPa, density of 860–1400 kg/m³, water absorption of 10–31% and porosity of 12–34%, and modulus of elasticity of 2.9–9.9 GPa were obtained. It can be used as lightweight geopolymer concrete for wall and partition.     

Styrene-acrylonitrile co-polymer impregnated mortar

The effect of radiation on the physical properties of styrene-acylonitrile co-polymer impregnated concrete was examined and compared with that of polymethyl methacrylate impregnated concrete. Monomer conversion, compressive and tensile strengths, molecular weight and water absorption were determined with changes in polymer loading. The impact strength and the acid resistance of styrene-acrylonitrile co-polymer impregnated specimens were also determined. Polymer loading was increased using vacuum and pressure impregnation techniques.     

Properties of high-performance LWAC for precast structures with Brazilian lightweight aggregates

An experimental study was carried out to examine five mixtures made with selected Brazilian lightweight aggregates in order to produce lightweight aggregate concrete (LWAC) for slim precast components. Flow (initial and after 2 h), air content, compressive strength, tensile strength (flexural and splitting), modulus of elasticity and deformation were studied. The 7-day compressive strength and the dry concrete density varied from 39.7 to 51.9 MPa and from 1460 to 1605 kg/m³, respectively. The results of this pilot study suggest that there are possibilities of producing slim precast components using high-performance lightweight concrete with Brazilian lightweight aggregates.     

Absorption and desorption properties of fine lightweight aggregate for application to internally cured concrete mixtures

Recently, substantial interest has developed in using fine lightweight aggregate for internal curing in concrete. Mixture proportion development for these mixtures requires the specific gravity, water absorption, and water desorption characteristics of the aggregate. This paper presents results from a recent study in which the properties of commercially available expanded shale, clay and slate lightweight aggregates (LWA’s) were measured. This research measured the time-dependent water absorption response for the lightweight aggregate. The results indicate that a wide range of 24 h water absorption values exist for commonly used fine lightweight aggregates (e.g., absorption between 6% and 31%). Desorption was measured and it was found that between 85% and 98% of the 24 h absorbed water is released at humidities greater than 93%. These properties can be normalized so that they can be efficiently used in proportioning concrete for internal curing. Normalized plots of absorption and desorption demonstrate benefits for a single function that describes a large class of expanded shale, clay, and slate aggregate for use in internal curing.     

空心球/铝基复合泡沫材料制备及性能研究

采用粉末冶金技术制备了不同孔隙率的空心球/铝基复合泡沫材料,对其进行T7热处理,并开展了不同孔隙率材料压缩性能及隔声性能的测试。结果表明,制备的泡沫材料中空心球均匀分布于基体内,且空心球与基体之间形成明显的过渡层;空心球/铝合金基复合泡沫材料的压缩应力-应变曲线呈现线弹性、应力平台、致密化3个阶段。随着孔隙率的增加,空心球/铝合金基复合泡沫材料的压缩峰值应力、平台应力及能量吸收能力均呈先上升后下降的变化趋势;随着孔隙率的增加,复合泡沫材料隔声性能逐渐下降。     

Durability aspect of concretes composed of cold bonded and sintered fly ash lightweight aggregates

This study reports the finding of an experimental study carried out on the durability related properties of the lightweight concretes (LWCs) including either cold bonded (CB) or sintered (S) fly ash aggregates. CB aggregate was produced with cold bonding pelletization of class F fly ash (FA) and Portland cement (PC) while S aggregate was produced by sintering the fresh aggregate pellets manufactured from FA and bentonite (BN). Two concrete series with water-to-binder (w/b) ratios of 0.35 and 0.55 were designed. Moreover, silica fume (SF) with 10% replacement level was also utilized for the purpose of comparing the performances of LWCs with and without ultrafine SF. The durability properties of concretes composed of CB and S aggregates were evaluated in terms of water sorptivity, rapid chloride ion permeability, gas permeability, and accelerated corrosion testing after 28 days of water curing period. The compressive strength test was also applied to observe the strength level at the same age. The results revealed that S aggregate containing LWCs had relatively better performance than LWCs with CB aggregates. Moreover, the incorporation of SF provided further enhancement in permeability and corrosion resistance of the concretes.