Self-compacting Lightweight Aggregate Concrete Research Articles

The microscopic fracture model for determining the fracture behavior of self-compacting lightweight concrete

The fracture toughness (KIC) and tensile strength (ft) of concrete are critical parameters governing crack resistance. Concrete usually exhibits brittleness under flexure and tension, so this brittle fracture first occurs at the micro level. Many researchers have studied its fracture properties at the micro level. However, the theoretical model and calculation formulae do not reflect the influence of micro-material parameters on the corresponding fracture properties. In this paper, the microscopic fracture model of self-compacting lightweight aggregate concrete (SCLC) was developed, considering the parameters of micro-nano silica materials. First, the characteristic parameters, such as particle size, specific surface area, and unit weight of micro silica (MS) and colloidal nano-silica (CNS), were considered, and the calculation equation for fictitious crack growth length was proposed. Then, the micro-fracture model was developed, which was further used to calculate the fracture parameters KIC and ft of SCLC incorporated with micro-nano silica. The results are found to be consistent with the fracture parameters determined by the size effect model. In addition, the failure curves of different structural fracture modes of SCLC were established through the fracture parameters KIC and ft obtained from the microscopic fracture model, and the fracture modes of SCLC incorporated with MS and CNS were identified. The peak load of the minimum specimen size satisfying linear elastic fracture was also predicted. This research provides a new perspective for evaluating concrete fracture parameters, realizes the progressive prediction of concrete fracture performance from macro to micro, and fills in the research gaps in the existing knowledge base on the synergistic effect of MS and CNS to enhance the fracture performance of SCLC.

Axial compression behavior of thin-walled steel partially encased fibre-reinforced self-compacting lightweight aggregate concrete columns

This study presents the mixture design method of fibre-reinforced self-compacting lightweight aggregate concrete (FSLC) and combines it with cold-formed steel (CFS) to propose a novel thin-walled steel partially encased FSLC (TPEC) column. The axial compression behavior of the TPEC column was revealed by test and finite element analysis. The test results showed that FSLC did not experience brittle failure when constrained by CFS. The presence of FSLC in CFS also restricted the occurrence of buckling, resulting in improved ductile behavior of the TPEC columns. However, the connection between the web separated at the peak load, at which time the column no longer satisfied the requirements for the serviceability limit state. Finite element analysis demonstrated the transverse constraint effect of the thin-walled steel frame on FSLC, and through parametric analysis, more rational arrangements for web connections can be obtained. The cross-section of the TPEC column can be divided into three constraint zones based on the strength of the transverse constraint on the FSLC. A compressive strength calculation model for FSLC under the constraint of a thin-walled steel frame was proposed. A calculation method of the axial carrying capacity of the TPEC column was proposed, and the corresponding calculation model demonstrated better applicability.

Thermal resistance, water absorption and microstructure of high-strength self-compacting lightweight aggregate concrete (HSSC-LWAC) after exposure to elevated temperatures

An experimental investigation on the influence of elevated temperatures on the thermal resistance, water absorption and microstructure of high-strength self-compacting lightweight aggregate concrete (HSSC-LWAC) is presented. In total, 315 concrete specimens from 7 different mixtures with different replacement ratios (0, 30 %, 50 % and 100 % by weight) of two kinds of LWAs, namely cloud concrete stone (CCS) and fly ash ceramsite (FAC), were prepared. The workability of fresh concrete mixtures including slump, J-Ring and T500 tests was first conducted aiming at meeting the requirements of self-compacting performance. Hardened concrete specimens were then exposed to different elevated temperatures (i.e. 200 °C, 400 °C, 600 °C and 800 °C) increased with a heating rate of 10 °C/min. A series of tests including the apparent morphology, ultrasound pulse velocity (UPV), residual compressive strength and capillary water absorption were carried out on unheated control concrete and after air-cooling period of heated concrete. Finally, the thermal analysis and microstructural observation were further conducted through the thermogravimetry (TG), differential scanning calorimetry (DSC), mercury intrusion porosimetry (MIP), laser scanning microscopy (LSM) and scanning electron microscope (SEM) to characterize the evolution of high temperature damage. Generally, the high temperature resistance of HSSC-LWAC shows an increasing trend as the LWAs content increases, while the residual mechanical strength increases and then decreases with an increase of the temperature gradient. The microstructural observation indicates that the evolution behavior of thermal damage promotes the continuous development of micropores in the interfacial transition zones (ITZ) to form wider microcracks, resulting in the degradation of residual mechanical properties.

Compressive behavior of CFRP-confined steel fiber-reinforced self-compacting lightweight aggregate concrete in square columns

Self-compacting lightweight aggregate concrete (SLC) is greatly limited in the application of tensile and high-shear structures due to its obvious brittleness and low elastic modulus. Therefore, carbon fiber-reinforced polymer (CFRP)-confined steel fiber-reinforced self-compacting lightweight aggregate concrete (SFSLC) square columns were proposed, and axial compression tests were conducted in this paper. The effects of the steel fiber content, CFRP layers, and compressive strength grade of core concrete on the mechanical properties of SLC square columns were studied. According to the experimental phenomena and stress–strain curves, the synergistic effect of steel fiber and CFRP can obviously improve the failure mode and mechanical properties after peak stress. In contrast, the synergistic effect of the steel fiber and CFRP would be weakened by increasing the compressive strength grade of the core concrete. With the increase in steel fiber content, the deformability of the core concrete was improved, which increased the lateral confinement effect of the CFRP. When the number of CFRP layers was small, the mechanical properties of the specimens were significantly improved by adding a small number of steel fibers. With the increase in the number of CFRP layers, the reflection of internal defects caused by excessive steel fibers could be decreased. Based on the experimental study, the influence of variables on the confinement effect was analyzed, and the influence coefficient λ of steel fiber on the deformation of the specimen was introduced to establish the stress–strain curve models of CFRP-confined SFSLC square columns. Compared with the experimental curve, the model has higher prediction accuracy.

Mixture design method of self-compacting lightweight aggregate concrete based on rheological property and strength of mortar

Self-compacting lightweight aggregate concrete (SCLC) is a kind of high performance concrete developed by combining the favourable properties of self-compacting concrete (SCC) and lightweight concrete (LWC). However, due to the lack of a mixture design method, its application in civil engineering is limited. Based on this, a new mixture design method taking the mortar film thickness as the key technical index was proposed. In this method, the mixture design procedure was divided into a self-compacting performance design based on the rheology of mortar and a strength design based on the effective water-cement ratio rule of mortar. By correlating the relationship between the workability and mortar rheological parameters and between strength and corresponding mortar strength, the mortar rheology and strength could be used to predict SCLC workability and strength. To verify the feasibility of this method, the self-compacting performance was designed by taking SCLC-1.8–0.35 as an example, and the strength was predicted by taking SCLC-1.8–0.3, SCLC-1.8–0.4 and related cases in the published literature as examples. This result indicated that this new design method could use the rheology and strength of mortar to predict the workability and strength of SCLC. • Mortar film thickness is the key technical index of the new mix design method. • Self-compacting performance of SCLC is designed based on mortar rheology. • Strength design of SCLC is designed based on effective water-cement ratio of mortar. • New method can predict SCLC workability and strength by using mortar properties.

Flexural toughness and evaluation method of steel fiber reinforced self-compacting lightweight aggregate concrete

The main purpose of this study was to investigate the effect of steel fiber on the flexural toughness of steel fiber reinforced self-compacting lightweight aggregate concrete (SFSLC). The applicability of the flexural toughness evaluation method specified in ASTM C1609 and JG/T 472-2015 for SFSLC was investigated. Test results showed that the evaluation methods in ASTM C1609 and JG/T 472-2015 were not suitable for evaluating the flexural toughness of SFSLC due to its higher deflection than fiber reinforced normal concrete. A new flexural toughness evaluation method including four indexes was proposed and test results showed that this new method could effectively reflect the flexural performance of SFSLC.

Bond Behavior of Deformed Bars in Self-Compacting Lightweight Aggregate Concrete at Early Ages

AbstractSelf-compacting lightweight aggregate concrete (SCLC) has attracted growing attention because of its self-compacting performance and good workability, thus the mechanical properties of SCLC...

Study on mixture design method and mechanical properties of steel fiber reinforced self-compacting lightweight aggregate concrete

A new mixture design method of steel fiber reinforced self-compacting lightweight aggregate concrete (SFSLC) based on paste film thickness theory and combination method was proposed in this study. In order to verify the feasibility of the proposed mixture design method, two types of SFSLC were designed and prepared. The effect of steel fiber content on the workability and mechanical properties including compressive strength, splitting tensile strength and flexural toughness performance of self-compacting lightweight aggregate concrete (SLC) was studied. The results showed that this new mixture method could quantitatively determine the content of raw materials. The addition of fiber reduced the filling ability and passing ability of SLC, but improved the segregation resistance of SLC. The improvement effect of micro-steel fiber on the mechanical properties such as compressive strength, splitting tensile strength and flexural toughness of SLC was significantly better than that of long steel fiber.

A New Composite Slab Using Crushed Waste Tires as Fine Aggregate in Self-Compacting Lightweight Aggregate Concrete.

A composite slab comprised of self-compacting rubber lightweight aggregate concrete (SCRLC) and profiled steel sheeting is a new type of structural element with a series of superior properties. This paper presents an experimental research and finite element analysis (FEA) of the flexural behavior of composite slabs consisting of SCRLC to develop a new floor system. Four composite slabs specimens with different shear spans (450 mm and 800 mm) and SCRLC (0% and 30% in rubber particles substitution ratio) are prepared, and the flexural properties including failure modes, deflection at mid-span, profiled steel sheeting, and concrete surface stain at mid-span and end slippage are investigated by four-point bending tests. The experimental results indicate that applying SCRLC30 in composites slabs will improve the anti-cracking ability under the loading of composite slabs compared with composite slabs consisting of self-compacting lightweight aggregate concrete (SCLC). FEM on the flexural properties of SCRLC composites slabs show that the yield load, ultimate load, and deflection corresponding to the yield load and the ultimate load of composite slabs drop as the rubber particles content increases in SCRLC. The variation of SCRLC strength has less impact on the flexural bearing capacity of corresponding composite slabs. Based on the traditional calculated method of the ultimate bending moment of normal concrete (NC) composite slabs, a modified calculated method for the ultimate bending moment of SCRLC composite slabs is proposed.

Bond Behavior of Deformed Bars in Self-Compacting Lightweight Aggregate Concrete Subjected to Lateral Tensions

The bond performance of reinforcing bars to concrete, an indispensable factor in designing reinforced concrete structures, is deeply influenced by the stress states of surrounding concrete. In recent decades, although self-compacting lightweight aggregate concrete (SCLC) has gained popularity in architectural engineering, the bond stress-slip relationship of deformed bars in SCLC under lateral tension remains unknown. In this study, 179 pullout tests were performed to examine the local bond stress-slip behavior of deformed bars in SCLC. In addition, the effects of various parameters on the ultimate bond strength and the slip at the ultimate bond stress, as well as the residual bond strength, were analyzed quantitatively. The results showed that both the bond strength and slip at the ultimate stress decrease with the increase of lateral tension regardless of whether it is in pull-out or splitting failure mode. In addition, an empirical formula was proposed that gives a reasonable prediction of the measured bond stress-slip curve of the SCLC.

Experimental Study on Dynamic Performance of Self-Compacting Lightweight Aggregate Concrete under Compression

In order to study the dynamic characteristics of the self-compacting lightweight aggregate concrete (SCLC) under uniaxial compression, 10 different strain rates (10−5–10−1/s) were set up to examine the uniaxial compressive dynamic performance of ordinary concrete, lightweight aggregate concrete, and SCLC, respectively. The failure modes and stress-strain curves of the samples under different loading conditions were obtained through experiment. The dynamic characteristics of the SCLC were analyzed by comparing the failure modes and testing data under different loading conditions. The following conclusions are drawn: the failure modes of the SCLC belong to destruction of shale ceramsite, which are similar to that of the lightweight aggregate concrete. The peak stress and elastic modulus of the self-compacting lightweight aggregate gradually increase with the increase of the loading strain rate, but the extent of increase of the peak stress is lower than that of the ordinary concrete and lightweight aggregate concrete. Affected by the loading strain rate and the random coupling of concrete, the peak strain of the self-compacting lightweight aggregate shows a relatively discrete changing trend. At the same time, the compressive dynamic performance of the SCLC was analyzed from the perspective of failure mechanism with a quantitative point of view.

Multi-axial test and failure criterion analysis on self-compacting lightweight aggregate concrete

Abstract In order to study the mechanical properties of self-compacting lightweight aggregate concrete under complex stress, experimental research on multi-axial stress behavior of self-compacting lightweight aggregate concrete were conducted by using a large general triaxial test machine. Through multi-axial tests, failure morphology and stress-strain curves of self-compacting lightweight aggregate concrete under different lateral stresses were obtained. By extracting the stress-strain curve eigenvalues (peak stress and peak strain) and analyzing the failure morphology, and citing the relevant literature to compare and analyze the conclusions of multi-axial research on ordinary concrete and lightweight aggregate concrete, the multi-axial stress characteristics and failure mechanism of self-compacting lightweight aggregate concrete were studied. The results show that when the uniaxial compression and lateral stress values of self-compacting lightweight aggregate concrete are small, the biaxial compression-pressure failure morphology mainly exhibits the shear failure morphology, which is different from that of ordinary concrete and lightweight aggregate concrete. At the same time, the influence of lateral stress on self-compacting lightweight aggregate concrete is obviously stronger than that of ordinary concrete and lightweight aggregate concrete. The failure criterion of self-compacting lightweight aggregate concrete based on Kupfer biaxial failure criterion and octahedral stress space has certain applicability. The content studied in this paper has theoretical significance for the engineering application development of self-compacting lightweight aggregate concrete.

Self-compacting lightweight aggregate concrete in Vietnam

Self-Compacting Lightweight Aggregate Concrete (SCLC) is a new building material in Vietnam. The lightweight aggregates (keramsite) produced from expanded clay or slate is used for the SCLC. If dry Keramsite is used in making the concrete mixture, it will partly absorb water from the cement paste, which causes the slump loss of concrete mixture, increasing shrinkage of cement matrix in the concrete. With regard to Self-Compacting Structural Lightweight Aggregate Concrete (SCLC), the cement content used is significant, the ratio of Water to Binder is rather low, and the structure of cement paste is very dense. This does not only increase the autogenous shrinkage of concrete but also have influence on the effectiveness of external curing. Taking advantage of the special structure of Lightweight aggregate as Keramsite, internal curing can be performed in order to improve the quality of SCLC by wetting Keramsite before mixing with suitable water absorption.This paper presents some research results about SCLC, the incorporation of internal curing with other measures such as the use of dispersal fiber reinforcement, viscous stabilizing admixtures in order to restrain the segregation level of lightweight aggregates, reducing shrinkage and improving mechanical-physical properties of SCLC in the hot-humid climate condition of Vietnam. The research results show that, from selected materials, lightweight concretes with unit weight of 1600 - 1800 kg/m3, compressive strength of 30 - 35 MPa, good workability, capable of self-compacting can be manufactured. The use of pre-wetted lightweight aggregate with suitable humidity for producing SCLC will result in better effectiveness than the use of dry lightweight aggregate, as in reducing restraining shrinkage, improving the strength for SCLC.

Bond-Slip Response of Plain Bars Embedded in Self-Compacting Lightweight Aggregate Concrete under Lateral Tensions

AbstractRecently, self-compacting lightweight aggregate concrete (SCLC) has been increasingly used in civil engineering. The bond behavior between plain bars and SCLC is an indispensable factor in ...

Effect of nano silica on the workability of self-compacting concretes having untreated and surface treated lightweight aggregates

This paper presents the fresh properties of self-compacting lightweight aggregate concrete (SCLC) made with cold bonded fly ash (FA) lightweight aggregate (LWA) at a wide range of water-to-binder (w/b) ratios. For this, three concrete series including eighteen SCLCs were designed with w/b ratios of 0.25, 0.37 and 0.50, respectively. Each series have 6 different mixes in which two type of coarse LWAs (surface treated or not) and three nano silica (nS) replacement levels (0, 2.5% and 5.0%) are considered. The properties of SCLCs were observed in terms of slump flow diameter, T500 slump flow time, V-funnel flow time, and L-box height ratio. The compressive strength test was also conducted to obtain the strength level at 28days. It is found that the fresh SCLCs have good fluidity, passing ability, uniform aggregate distribution and resistance to segregation. Incorporating treated coarse LWAs increased the workability characteristics of SCLCs. However, appreciable improvement in the consistency of SCLCs by nS addition was observed. The SCLCs made with treated LWAs and 5% nS were found to be the harder samples in this research.

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.

The effect of pumice powder on the self-compactability of pumice aggregate lightweight concrete

This paper presents the results of an experimental study about the effects of pumice powder, 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 aggregates. 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 investigated. For this purpose, 24 series of concrete samples were prepared in two groups. In the first group, pumice aggregate at the rate of 100% was used for 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 the 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 with fly ash and blast furnace slag mineral additives at the constant rate of 40%. The 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 in the range of 560–800mm, 2–11s, 435–558l/m3, 10.5–65.0MPa, 840–2278kg/m3, 0.347–1.694W/mK and 2611–4770m/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.

Physico-mechanical properties of self-compacting concrete containing treated cold-bonded fly ash lightweight aggregates and SiO2 nano-particles

In this experimental study, the physico-mechanical properties of self-compacting lightweight aggregate concrete (SCLC) containing artificial lightweight aggregate (LWA) made from fly ash (FA) through cold-bonded process are investigated. Coarse LWAs were treated with a soluble solution of sodium silicates (WG) in order to enhance quality. However, the binary and ternary use of fly ash (FA) and silicon dioxide nanoparticles (nS) were considered in the production of SCLC. For this, a total of 18 SCLC mixtures were designed at three different w/b ratios of 0.25, 0.37 and 0.50, and total binder contents of 600, 550 and 450kg/m3, respectively. The physical properties were tested for water sorptivity, gas permeability and water permeability, as well as for drying shrinkage. The use of treated instead of untreated LWA reduces the negative effect of w/b ratio increment of the drying shrinkage of SCLCs. The results showed that using 5.0% nano-silica and treated aggregate decreased the drying shrinkage as much as 23%. However, a significant reduction in SCLC permeability was achieved by including nS and/or treated LWAs, specifically, a reduction of up to 70% for gas permeability at 90days. Moreover, a lower compressive strength resulted due to the use of untreated aggregate and higher w/b ratio. As a general result, it was determined that a better performance is revealed at 90days for SCLCs containing 5% nS and treated LWAs, regardless of w/b ratio.

Use of synthetic fibers in self-compacting lightweight aggregate concretes

In this work, fiber reinforced SCLWAC (self-compacting lightweight aggregate concrete) mixtures were studied, in which synthetic fibers were used. Eight different SCLWACs were prepared, in which, as aggregates, different combinations of fine and coarse expanded clay were tried, also partially replaced by either quartz sand or aggregate coming from concrete recycling. SCLWACs were characterized at the fresh state by means of slump flow, V-funnel and L-box tests, and after hardening by means of compression, splitting tension and bending tests, and drying shrinkage measurements. Strength class of LC 45/50 was obtained by using synthetic macrofibres when the oven dry density of SCLWAC was about 1600kg/m3, while if the oven dry density of SCLWAC was lower than 1250kg/m3 a strength class of LC 25/28 was reached as well. Tensile and flexural strength values were consistent with concrete strength class, while the elastic modulus was quite low with respect to normal weight self-compacting concrete (SCC). The post-cracking behavior of SCLWAC was strongly improved by the addition of synthetic macrofibers, which provided strain-hardening effect similar to that achievable by means of steel fibers, even if characterized by a sensibly lower weight. In conclusion, SCLWACs showed excellent combination of mechanical and functional properties.

The effect of fly ash to self-compactability of pumice aggregate lightweight concrete

This paper presents the results of an experimental study on the effects of fly ash, different water/(cement + mineral additive) ratios and pumice aggregates to some physical and mechanical properties of self-compacting lightweight aggregate concrete. In this study, pumice had been used as lightweight aggregates. Several properties of self-compacting pumice aggregate lightweight concretes like the 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 investigated. For this purpose, 18 series of concrete samples were prepared in two groups. Pumice aggregate was used as a replacement of natural aggregate, at the levels of 0, 20, 40, 60, 80, and 100% by volume. Furthermore, a second series of 100% pumice aggregate was used for the production of self-compacting lightweight aggregate concrete with constant w/(c + m) ratios as 0.35, 0.40, and 0.45 by weight. The flow diameters, T50 times, paste volumes, 28-day compressive strengths, dry unit weights and thermal conductivities of self-compacting lightweight aggregate concrete were obtained in the range of 600–800 mm, 2–8 s, 471–572 lt/m 3, 9.2–53.26 MPa, 839–2156 kg/m 3 and 0.321–1.508 W/mk, 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.