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.     

Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete

This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.     

Workability and strength behaviour of concrete with cold-bonded fly ash aggregate

This paper discusses the development of empirical models for workability and compressive strength of cold-bonded fly ash aggregate concrete in terms of mixture proportioning variables such as cement content, water content and volume fraction of cold-bonded aggregate through statistically designed experiments based on Response Surface Methodology. Factor level of cement is taken from 250 to 450 kg/m³ to introduce weak as well as strong matrix phase in the concrete. Apart from water content, workability of concrete is highly influenced by main and interaction effect of volume fraction of cold-bonded aggregate in the composition. Response surface indicate that increase in cement content causes to change the predominant failure mode from mortar failure to aggregate fracture and concrete strength decreases with increase in volume fraction of aggregate at higher cement contents. The models developed have been found useful in arriving typical relationship to establish a mixture proportioning methodology for cold-bonded fly ash aggregate concrete.     

Influence of fly ash as a cement addition on the hardened properties of recycled aggregate concrete

The effects of the use of Class F fly ash as a cement addition on the hardened properties of recycled aggregate concrete were determined. In this study, four series of concrete mixtures were prepared with water-to-cement (w/c) ratios of 0.55, 0.50, 0.45 and 0.40. The recycled aggregate was used as 0%, 20%, 50% and 100% replacements of coarse natural aggregate. Furthermore, fly ash was employed as 0% and 25% addition of cement. Although the use of recycled aggregate had a negative effect on the mechanical properties of concrete, it was found that the addition of fly ash was able to mitigate this detrimental effect. Also, the addition of fly ash reduced the drying shrinkage and enhanced the resistance to chloride ion penetration of concrete prepared with recycled aggregate. Moreover, it was found that the drying shrinkage and chloride ion penetration decreased as the compressive strength increased. Compared with the results of our previous study, the present study has quantified the advantages of using fly ash as an additional cementitious material in recycled aggregate concrete over the use of fly use as a replacement of cement.     

Properties of hardened concrete containing treated expanded polystyrene beads

This paper reports the results of an experimental investigation into the properties of hardened concrete containing chemically treated expanded polystyrene beads. The results showed that the strength, stiffness and chemical resistance of polystyrene aggregate concrete of a constant density were affected by the water to cement ratio. Drying shrinkage after 84 days of drying for polystyrene concretes, having 10 mm coarse aggregate and a nominal density of 1300 kg/m³, were 730 and 655 microstrains. Empirical equations were developed to relate the strength and pulse velocity and to predict the modulus of elasticity from its strength.     

Effect of carbonation of modeled recycled coarse aggregate on the mechanical properties of modeled recycled aggregate concrete

The modeled recycled aggregate concrete (MRAC) which is an idealized model for the real recycled aggregate concrete (RAC) was used in this study. The MRCAs prepared with two types of old mortars were modified by an accelerated carbonation process. The effects of carbonation of MRCA on the micro-hardness of MRCA and the mechanical properties of MRAC were investigated. The results indicated that the micro-hardness of the old interfacial transition zone (ITZ) and the old mortar in the carbonated MRCAs was higher than that in the uncarbonated MRCAs, and the enhancement of the old ITZ was more significant than that of the old mortar. The compressive strength and modulus of MRACs increased when the carbonated MRCAs were utilized, and the improvement was more significant for MRAC prepared with a higher w/c. In addition, a numerical study was carried out and it showed that the improvement in strength by carbonation treatment was less obvious when the difference between the new and old mortar was larger.     

Effects of portland cement replacement with limestone on the properties of hardened concrete

Limestone portland cement has a lower environmental impact during the production phase in comparison with portland cement. However, the environmental advantages initially gained should be correlated to the long-term performance of concrete structures. Hence, the knowledge of the long-term properties, and in particular durability performance, is essential to assess the actual environmental impact of limestone replacement. In the literature, there is disagreement on durability behaviour and the contribution of limestone to the resistance to chloride and carbonation penetration is controversial. In this paper, the effect of the percentage of replacement of portland cement with ground limestone, water/binder ratio and cement content on compressive strength, electrical resistivity, sorptivity and resistance to carbonation and chloride penetration was evaluated. Results showed that both mechanical properties and resistance to penetration of aggressive agents decreased by replacing 15% of portland cement with limestone; a further decrease occurred with 30% limestone.     

Proportioning and characterization of lightweight concrete mixtures made with rigid polyurethane foam wastes

This paper presents the results of an experimental study concerning the incorporation of polyurethane (PUR) foam wastes into cementitious mixtures in order to produce lightweight concrete. A semi-empirical method is first proposed to predict the density of fresh PUR foam-based concrete mixtures. Seven concrete mixtures containing various PUR foam volume fractions (from 13.1% to 33.7%), and two reference concrete mixtures (without PUR foam) were prepared and characterized. In particular, their thermal and mechanical properties were determined. This permitted to quantify the influence of the PUR foam volume fraction on these parameters. Some specimens were maintained under water during 28 days, while the others were dried in air. The PUR-foam concrete thermal conductivity and compressive strength are, respectively, 2–7 times and 2–17 times lower than those of the reference mixture, depending on the volume fraction of PUR foam and on the curing conditions. Besides, the use of PUR foam in concrete implies a strong increase in the drying shrinkage and in the mass loss during the first seven days. These results can be related to the high porosity and the weak compressive strength of alveolar polyurethane.     

Effect of environmental conditions on the properties of fresh and hardened concrete

The effect of varying environmental conditions, at the time of casting on the properties of fresh and hardened concrete was evaluated. The influence of air temperature, wind velocity, and relative humidity on plastic shrinkage, compressive strength, pulse velocity and pore structure of concrete was investigated. Results indicate that exposure conditions at the time of casting significantly affect plastic shrinkage of concrete. As expected elevated temperature affected porosity, compressive strength, and pulse velocity of concrete. Casting of concrete at elevated temperature decreased its compressive strength. Similarly, the pulse velocity of concrete cast at 45°C was less than that of cast at 30°C. The volume of total pores in the concrete specimens cast at 45°C was more than that of cast at 30°C. The lower pulse velocity and increased pore volume in the concrete cast at 45°C than that cast at 30°C may be attributed to the coarse pore structure formed in the former than the latter. Other weather parameters, such as relative humidity and wind velocity, also influence the properties of fresh and hardened concrete.     

石灰石粉对泵送混凝土性能影响的试验研究

本文主要研究了单掺石灰石粉、石灰石粉与粉煤灰复掺对泵送混凝土拌合物工作性和抗压强度的影响,研究表明：掺加石灰石粉可以改善泵送混凝土的工作性能,与单掺石灰石粉相比,石灰石粉与粉煤灰复掺,具有复合叠加效应,不仅可以改善泵送混凝土的工作性能,同时可提高泵送混凝土的抗压强度。     

Effect of metakaolin on creep and shrinkage of concrete

The effect of metakaolin (MK) on the creep and shrinkage of concrete mixes containing 0%, 5%, 10%, and 15% MK has been investigated. The results showed that the early age autogenous shrinkage measured from the time of initial set of the concrete was reduced with the inclusion of MK, but the long-term autogenous shrinkage measured from the age of 24 h was increased. At 5% replacement level, the effect of MK was to increase the total autogenous shrinkage considered from the time of initial set. While at replacement levels of 10% and 15%, it reduced the total autogenous shrinkage. The total shrinkage (autogenous plus drying shrinkage) measured from 24 h was reduced by the use of MK, while drying shrinkage was significantly less for the MK concretes than for the control concrete. The total creep, basic creep as well as drying creep were significantly reduced particularly at higher MK replacement levels. Compared with estimated values by the CEB 90 model, total creep of all concretes was overestimated, especially in the mixes containing the higher levels of MK. For basic creep, estimates for low levels of MK were acceptable but, for the higher levels, creep was overestimated.     

Optimum content of copper slag as a fine aggregate in high strength concrete

This study investigated the mechanical properties of high strength concrete incorporating copper slag as a fine aggregate and concluded that less than 40% copper slag as sand substitution can achieve a high strength concrete that comparable or better to the control mix, beyond which however its behaviors decreased significantly. The workability and strength characteristics were assessed through a series of tests on six different mixing proportions at 20% incremental copper slag by weight replacement of sand from 0% to 100%. The results indicated that the strength of the concrete with less than 40% copper slag replacement was higher than or equal to that of the control specimen and the workability even had a dramatic growth. The microscopic view demonstrated that there were limited differences between the control concrete and the concrete with less than 40% copper slag content. It also suggested that the determination of the copper slag replacement level should consider with the desired compressive strength of concrete.     

Properties of autoclaved aerated concrete incorporating rice husk ash as partial replacement for fine aggregate

This study examines the effects of rice husk ash (RHA) on the physical, mechanical and microstructural properties of autoclaved aerated concrete (AAC) produced at a temperature of 180 °C for 8 h and 18 h. The RHA was used as an aggregate at various replacement ratios. The results demonstrated that RHA substitution for sand reduces compressive strength and unit weight. In terms of the microstructure, the highly reactive silica in RHA strongly affected the tobermorite transformation. At 8 h of autoclaving time, the lath-like and plate-like tobermorite formed in mixtures containing up to 50% RHA was replaced by a glass-like, silica-rich CSH structure at increased replacement ratios. However, extended processing had no significant effect on these properties, which indicates that the substitution of RHA for sand has a tendency to reduce the autoclaving time or autoclaving temperature required.     

Mechanical properties of concrete containing phase-change material

This study aimed to investigate the mechanical properties of concrete containing solid–liquid phase-change material (PCM) and focused on two key factors. First, a systematic study on the mechanical performance of PCM-modified concretes was conducted, including compressive, elastic modulus, and shrinkage tests. Second, because PCM provides high latent heat during the solid–liquid phase change, the effects of the solid phase and liquid phase on the mechanical properties of concrete were also explored. Results of this study showed that the solid–liquid phase of PCM affected the mechanical properties of concrete. For example, the compressive strength of 10% PCM concrete in solid phase (23 °C) and liquid phase (40 °C) at 28 days was 29.30 and 19.57 MPa, respectively. In addition, with increasing PCM content, the mechanical properties were degraded. For example, 10, 20, and 30% of PCM content lowered the compressive strength by 35.4, 58.4, and 74.3%, respectively. Therefore, concrete with PCM may not be suitable for structural elements. However, PCM is an important solution for optimizing energy consumption in modern buildings. It can absorb or emit large amounts of heat to store or release thermal energy. These properties can be used to control building temperatures resulting in energy saving and carbon reduction.     

A comparison study of the mechanical properties and drying shrinkage of oil palm shell and expanded clay lightweight aggregate concretes

For making artificial lightweight aggregate, selected raw materials are fed into a rotary kiln at high temperature. Providing such a high temperature is costly and generally, the process of making artificial lightweight aggregate is not environmentally friendly. The use of natural lightweight aggregate for making lightweight concrete can lead to low-cost construction. The use of a solid waste lightweight aggregate namely oil palm shell (OPS) as coarse aggregate, is not only environmentally friendly but leads to a low-cost material. This study is a comparison between some engineering properties of OPS lightweight concrete and an artificial lightweight (expanded clay) concrete with low water to cement ratio, along with having good workability and without any segregation. The test results show that OPS concrete has better mechanical properties and a higher efficiency factor than expanded clay lightweight concrete. The ceiling strength of expanded clay lightweight concrete occurs at an early age; while it happens in OPS concrete at a later age. The crack pattern of the tested specimens shows that OPS is much stronger than expanded clay. On the other hand, the compressive strength of OPS lightweight concrete is more sensitive to lack of curing. Although OPS lightweight concrete shows twice the amount of drying shrinkage than expanded clay lightweight concrete in the short term, this difference reduces significantly at later ages.     

Influence of steam curing on the pore structures and mechanical properties of fly-ash high performance concrete prepared with recycled aggregates

In this research work, High Performance Concrete (HPC) was produced employing 30% of fly ash and 70% of Portland cement as binder materials. Three types of coarse recycled concrete aggregates (RCA) sourced from medium to high strength concretes were employed as 100% replacement of natural aggregates for recycled aggregate concrete (RAC) production. The specimens of four types of concretes (natural aggregate concrete (NAC) and three RACs) were subjected to initial steam curing besides the conventional curing process. The use of high quality RCA (>100 MPa) in HPC produced RAC with similar or improved pore structures, compressive and splitting tensile strengths, and modulus of elasticity to those of NAC. It was determined that the mechanical and physical behaviour of HPC decreased with the reduction of RCA quality. Nonetheless steam-cured RACs had greater reductions of porosity up to 90 days than NAC, which led to lower capillary pore volume.     

How do recycled concrete aggregates modify the shrinkage and self-healing properties?

This paper presents the main results of a research carried out to analyze the mechanical properties, intrinsic permeability, drying shrinkage, carbonation, and the self-healing potential of concrete incorporating recycled concrete aggregates. The recycled concrete mixtures were designed by replacing natural aggregates with 0%, 30%, and 100% of recycled concrete gravel (RG) and 30% of recycled concrete sand (RS). The water to equivalent binder ratio was kept constant and recycled concrete aggregates were initially at saturated surface dried (SSD) state. The contribution of the porosity of natural and recycled aggregates to the porosity of concrete was estimated to understand the evolution of the intrinsic permeability and the open porosity. At long term, the maximum variation of drying shrinkage magnitude due to recycled concrete gravels did not exceed 15%. The correlation between drying shrinkage and mass-loss through “drying depth” concept showed that recycled concrete aggregates are affected by drying as soon as concrete is exposed to desiccation. A good correlation between 1-day compressive strength and 18-month carbonation depth was observed. The recycled concrete aggregates presented a good potential for self-healing as the relative recovery of cracks reached up to 60%.     

Specific surface area of aggregate and its relation to concrete drying shrinkage

This paper deals with the influence of aggregate properties on the shrinkage of concrete during drying. The drying shrinkage strains of concretes with various types of aggregates were measured and their influences on the fundamental properties of the different types of aggregates were investigated. Furthermore, the specific surface areas (SSAs) of aggregates were obtained by the BET method using both nitrogen (N₂) and water vapour (H₂O). The SSAs determined by using H₂O exhibited higher values than those by using N₂. The drying shrinkage strains of concretes increased with the H₂O SSAs of the aggregates used. Our results suggest that the SSA determined by using H₂O is an effective index for evaluating the influence of the aggregate type on the drying shrinkage of concrete.     

Bond strength prediction for deformed steel rebar embedded in recycled coarse aggregate concrete

This paper summarizes the results of an experimental investigation into the bond behavior between recycled aggregate concrete (RAC) and deformed steel rebars, with the main variables being the recycled coarse aggregate replacement ratio (RCAr) and water-to-cement ratio of the concrete mixture. The investigation into splitting cracking strength indicates that the degradation of the bond splitting tensile stress of the cover concrete was affected by not only the roundness of the coarse aggregate particles but also the weak interfacial transition zone (ITZ) between the cement paste and the RCA that has a more porous structure in the ITZ than normal concrete. In this study, a linear relationship between the bond strength and the density of the RCA was found, but the high compressive strength reduced the effects of the parameters. To predict the bond strength of RAC using the main parameters, a multivariable model was developed using nonlinear regression analysis. It can be inferred from this study that the degradation characteristic of the bond strength of RAC can be predicted well, whereas other empirical equations and code provisions are very conservative.     

Effect of cement type and limestone particle size on the durability of steam cured self-consolidating concrete

This paper describes a laboratory program to investigate the influence of cement and limestone filler (LF) particle size on the hardened properties and durability performance of steam cured self-consolidating concrete. In addition, the interplay between cement type and LF particle size was investigated. CSA (Canadian Standards Association) Type GU (General Use) and HE (High Early-strength) cements were used with 5% silica fume (SF) [1]. The water-to-cement ratio was 0.34. LF with two nominal particle sizes of 17 μm and 3 μm, which correspond to Blaine fineness of 475 and 1125 m²/kg, respectively, were used. In addition to fresh concrete properties, hardened properties including compressive strength, elastic modulus, ultrasonic pulse velocity and density were measured at 12 h and 16 h, and at 3, 7 and 28 days. Indicators of durability performance including rapid chloride permeability testing (RCPT), sulfate resistance, linear shrinkage, salt scaling resistance and freeze-thaw resistance were evaluated. The results showed that LF improved the 12 and 16-h strength with no influence on later age strength (i.e., 3–28 days). The linear shrinkage and RCPT decreased with the addition of LF. This reduction was linked to the production of calcium mono-carboaluminate. LF did not impact the sulfate resistance, salt scaling resistance or freeze-thaw resistance of concrete.