Internal structure examination of lightweight concrete produced with polymer-coated pumice aggregate

In the construction sector, pumice is observed to be used in both structural and non-structural building elements. In this study, to produce a new kind of concrete, the aggregates are coated with three different polymers (Sonomeric1: SNMC, KB Pur 214: KBP and Polipol3455: PLP) that have multiple uses. The mineralogical-petrographical features of both polymer-coated and uncoated aggregates were examined, and SEM (Scanning Electron Microscope) and XRD (X-ray Diffraction) analyses were performed. Moreover, in the study, lightweight concrete elements with different dosages (300, 400 and 500) were produced by using polymer-coated and uncoated aggregates; and their internal structure examinations were performed and compressive strength values of 3, 7 and 28 days samples were investigated. As a conclusion; among the aggregate samples, it was determined that PLP-coated aggregates have a more porous structure than the other polymer-coated aggregates and KBP-coated aggregates could be used in lightweight concrete (500 dosage) production. It was also concluded that the compressive strength values of lightweight concrete elements produced with coated samples increased even more.     

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.     

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.     

The use of pumice lightweight concrete for masonry applications

In the last two decades, the use of pumice as lightweight aggregate for concrete in structural applications has been the object of different studies. The aim was to find out if pumice can be an alternative to ordinary lightweight aggregate. The present paper is framed in this context. Here, a study is presented showing the use of pumice for making lightweight concrete units for masonry members. Through the paper, the formulation of a mix design for lightweight concrete is proposed. Then the obtained mechanical characteristics of the masonry units are discussed and compared to the code requirements. Reinforced bearing masonry walls, made with the concrete masonry units in question, were made and tested under lateral cyclic loads. For comparison, lightweight concrete units and bearing walls made using expanded clay were constructed and tested in order to show if pumice can also be considered as an alternative to ordinary lightweight aggregate in the case discussed here.     

Shear transfer capacity along pumice aggregate concrete and high-performance concrete interfaces

This paper aims to present an experimental investigation on the behaviour of interfaces between pumice LWAC (lightweight aggregate concrete) and HPC (high-performance concrete-high-strength and fibre-reinforced), typically found in the faces and core, respectively, of hybrid precast structural sandwich panels. The evaluation of the experimental data resulted in the derivation of a semi-empirical relationship that relates the interface strength with materials strength, interface geometry and loading parameters. A brief overview of existing shear friction theories and proposed relationships, as well as a somparison among existing models and that proposed by the authors, are also outlined in the paper.     

A simple mix design method for structural lightweight aggregate concrete

Current design methods for structural lightweight aggregate concrete (SLWAC) are usually only valid for a limited range of concrete compositions that have previously been subjected to trial tests. The SLWAC mix design is more complex than that of normal weight concrete as more parameters need to be determined. Taking this into account, a simplified design method is proposed for SLWAC made with natural sand. The major advantages of the proposed method are that it is easy to apply and it can be generalized to any type of lightweight aggregate (LWA). For this, three additional design parameters are needed: the strength of LWA in concrete; the limit strength; the SLWAC potential strength. At most, two experimental mixtures are needed to determine these parameters. A biphasic model to estimate the strength of SLWAC is evaluated and high correlations are obtained. The good performance of the suggested method is demonstrated by examples of practical application and by the comparison with experimental results reported by the authors and other investigators.     

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.     

Interdependence of microstructure and strength of structural lightweight aggregate concrete

The demand for lightweight concrete is steadily increasing because of economic and practical considerations. Hence, the inherent internal and external features of lightweight aggregates have been a subject of intense research in recent years. This study provides new insight into the micro-structural and chemical factors which influence the strength properties of structural lightweight aggregate concrete. These are described with respect to four expanded clay lightweight aggregates used in nine concrete compositions containing various types and proportions of dispersing agents such as water-reducing admixtures and superplasticizers, with silica fume and ground granulated blast-furnace slag as optional mineral admixtures. The microstructural characteristics of the paste-aggregate interface and the paste porosity of these concretes are discussed. The methods used include scanning electron microscopy-energy-dispersive X-ray analysis, X-ray diffraction analysis, optical microscopy and compressive strength testing.     

自密实轻集料混凝土双轴受力力学性能

为探究自密实轻集料混凝土双轴力学性能,采用三轴试验机对其进行双轴压-压和双轴拉-压试验,得到不同工况下的应力-应变曲线及其破坏形态,通过提取应力-应变曲线峰值应力和峰值应变,并与相关文献普通混凝土与轻集料混凝土研究成果对比,分析自密实轻集料混凝土双轴力学性能。研究结果表明:双轴压-压工况下,当侧向压应力较低时,试件主要呈现剪切破坏形态;当侧向应力较高时,试件呈劈裂破坏形态。双轴拉-压工况下,试件主要呈劈拉破坏形态,与侧向应力无关。随着侧向压应力的提高,自密实轻集料混凝土主压应力相对比无侧向应力工况明显提高,峰值应力最大提高均值幅度为68.08%,主拉应力随侧向压应力的提高逐步降低,最大降低幅度为62.35%。应用Kupfer双轴受力破坏准则验证自密实轻集料混凝土受侧向应力影响变化规律较为保守,同时基于Kupfer提出自密实轻集料混凝土双轴力学性能破坏准则,所得到的破坏准则方程具有良好的适用性。      

Some characteristics of high strength fiber reinforced lightweight aggregate concrete

The effect of polypropylene and steel fibers on high strength lightweight aggregate concrete is investigated. Sintered fly ash aggregates were used in the lightweight concrete; the fines were partially replaced by fly ash. The effects on compressive strength, indirect tensile strength, modulus of rupture, modulus of elasticity, stress–strain relationship and compression toughness are reported. Compared to plain sintered fly ash lightweight aggregate concrete, polypropylene fiber addition at 0.56% by volume of the concrete, caused a 90% increase in the indirect tensile strength and a 20% increase in the modulus of rupture. Polypropylene fiber addition did not significantly affect the other mechanical properties that were investigated. Steel fibers at 1.7% by volume of the concrete caused an increase in the indirect tensile strength by about 118% and an increase in the modulus of rupture by about 80%. Steel fiber reinforcement also caused a small decrease in the modulus of elasticity and changed the shape of the stress–strain relationship to become more curvilinear. A large increase in the compression toughness was recorded. This indicated a significant gain in ductility when steel fiber reinforcement is used.     

Engineering properties of lightweight aggregate concrete made from dredged silt

Silt dredged from reservoirs can be hydrated and sintered into lightweight aggregate for producing lightweight aggregate concrete (LWAC). The densified mixture design algorithm (DMDA) was employed to manufacture LWAC using 150 kg/m³ of water at different water-to-binder ratios (w/b = 0.28, 0.32 and 0.4) using lightweight aggregates of different particle densities (800, 1100 and 1500 kg/m³). The engineering properties of the LWAC thus obtained were examined. Results show that the fresh concrete meets the design requirement of having slump of 250 ± 20 mm and slump flow of 600 ± 100 mm. With respect to hardened properties, the compressive strength, ultrasonic pulse velocity and thermal conductivity were found to decrease with increasing w/b ratio but increase with increasing aggregate density. Moreover, higher aggregate density also resulted in less shrinkage. The surface resistivity exceeding 20 kΩ-cm also matched the design objective. The experimental results prove that LWAC made from dredged silt can help enhance durability of concrete.     

Non-steady-state accelerated chloride penetration resistance of structural lightweight aggregate concrete

This study aims to characterise the chloride penetration resistance of structural lightweight aggregate concrete (LWAC) produced with different types, volumes and initial wetting conditions of lightweight aggregates (LWA), types of cement and contents of fly ash and silica fume, w/c ratios and curing conditions. A comprehensive experimental study was carried out involving three types of non-steady-state tests, which simulate different exposure conditions and penetration mechanisms. It is shown that the chloride penetration resistance is mainly affected by the cementitious paste and that high performance LWAC of 30–70 MPa can be produced. Regardless of the type of aggregate, we propose exponential relations to estimate the diffusion coefficient of chlorides. The volume and initial wetting condition of LWA had little influence on the chloride resistance. A long-term higher reduction of the diffusion coefficient was found in less dense LWAC. Reasonable correlations between the non-steady-state tests were obtained. Contrary to what is suggested in some European standards, the concrete strength cannot properly predict the durability behaviour of LWAC.     

Thermal properties of lightweight dry-mix shotcrete containing expanded perlite aggregate

This paper describes the thermal properties of lightweight dry-mix shotcrete using expanded perlite aggregate (EPA). Mixes made with different EPA/sand ratios were sprayed through the dry-mix shotcreting technique onto wooden molds to produce panels for mechanical and thermal testing. The density, uniaxial compressive strength (UCS), splitting tensile strength (STS), and the ultrasonic pulse velocity (UPV) were measured at various ages. Further, the ISO approved transient plane source (TPS) technique was employed to measure the thermal properties at 28 days. The results illustrate that shotcrete mixes with EPA have similar UCS and superior STS compared to cast concrete. Adding EPA led to a drop in thermal conductivity and diffusivity. When compared with cast concrete, shotcrete had lower specific heat capacity. This study found dry-mix shotcrete incorporating EPA at up to 75% sand substitution as a mechanically viable and thermally resistant alternative to cast concrete containing regular aggregates.     

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.     

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.     

预湿轻集料对混凝土内部相对湿度特性的影响

为缓解混凝土的早期自干燥,减小自收缩,用预湿轻集料对其内部相对湿度进行调控.采用湿度测试仪和混凝土收缩测试仪,研究了水胶比、矿物掺合料对混凝土内部相对湿度与自收缩的影响规律,及预湿轻集料对自收缩的抑制效果.研究表明:混凝土内部相对湿度早期下降快,后期下降慢;降低水胶比、掺加硅灰会加快内部相对湿度的下降速度,而粉煤灰的加入可延缓低水胶比混凝土早期内部相对湿度的下降过程.预湿轻集料的引入可对混凝土内部相对湿度起到补偿作用,减小自收缩,作用效果随轻集料引入水量的增大而增强.     

Manufacture and performance of lightweight aggregate from municipal solid waste incinerator fly ash and reservoir sediment for self-consolidating lightweight concrete

Reservoir sediment, as the main material, was blended with municipal solid waste incinerator (MSWI) fly ash (including cyclone ash and scrubber ash) to manufacture lightweight aggregates (LWAs) using a pelletizing disk, and then sintering in a rotary kiln. The selected LWA was used as coarse aggregate for producing self-consolidating lightweight concrete (SCLWC). The results show that the maximum content of MSWI fly ash should be less than 30%. LWA with specific gravity in the range of 0.88–1.69 g/cm³ and crushing strength as high as 13.43 MPa can be produced. SCLWCs showed excellent flow-ability without bleeding or segregation. The 28-day compressive strengths of the SCLWCs ranged between 25 and 55 MPa. The electrical resistivity and ultrasonic pulse velocity of the SCLWCs satisfied the required values of 8.5 kΩ cm and 3600 m/s, respectively. Therefore, the SCLWCs produced in this study have good corrosion resistance and can be classified as good quality.     

自密实轻骨料混凝土压-剪复合受力力学性能

为探究自密实轻骨料混凝土压-剪复合受力力学性能,应用液压伺服机和材料压-剪试验机,对自密实轻骨料混凝土进行单轴受压、单轴劈裂抗拉和压-剪复合受力试验研究,通过试验得到不同加载工况下自密实轻骨料混凝土破坏形态和力-变形曲线,引用文献对普通混凝土和轻骨料混凝土压-剪复合受力研究数据,对比分析自密实轻骨料混凝土压-剪复合受力性能。研究结果表明:自密实轻骨料混凝土压-剪复合受力破坏形态与普通混凝土和轻骨料混凝土相类似,随着轴压比的提高,剪切破坏断面摩擦痕迹逐步明显,混凝土碎渣也逐步提高,自密实轻骨料混凝土剪切破坏强度、残余荷载和剪切破坏位移也随之提高;剪切破坏强度提高幅度高于普通混凝土和轻骨料混凝土,残余荷载受轴压比影响提高幅度高于普通混凝土,但略低于轻骨料混凝土。基于主应力空间结合普通混凝土和轻骨料混凝土压-剪试验数据,提出混凝土压-剪复合受力统一破坏准则,同时基于八面体应力空间,提出自密实轻骨料混凝土破坏准则,所提出的破坏准则具有良好的适用性。