Normal Weight Aggregate Concrete Research Articles

Performance of steel fibre reinforced lightweight aggregate concrete in fresh and hardened state

Abstract There is a growing interest in the manufacture of lightweight aggregate concrete (LWC) due to its low density, which is below 2000 kg/m3. However, the trade-off for the lower density is a reduction in strength, leading to a drop in crack resistance. Therefore, steel fibre inclusion was implemented to augment the crack resistance of lightweight concrete (LWC). Thus, the present study aims to examine the impact of steel fibre on both the workability and mechanical properties of lightweight aggregate concrete (LWC) that incorporates lightweight expanded clay aggregate (LECA). Three varieties of concrete were fabricated, namely normal weight aggregate concrete (NC), lightweight concrete (LWC), and steel fibre lightweight concrete (SFWLC). The SFLWC incorporated hooked-end steel fibres as reinforcement, with fibre volume percentages of 1 % and 2 %. A strength assessment was undertaken to ascertain the concrete properties, with particular emphasis on compressive and tensile strength. The findings indicate that the incorporation of both LECA and steel fibre led to a notable reduction in the workability of concrete. Incorporating a 2 % steel fibre content into LWC yields a marginal enhancement in compressive strength. Steel fibre demonstrates enhanced efficacy when subjected to tension, with the most significant increase measured at around 152 %.

Enhancing Structural Performance: Fiber Reinforcement in Sintered Flyash Lightweight Concrete for Impact Resistance and Toughness

Objectives: The goal of this project is to better understand the interaction between fibers and concrete in order to produce Light Weight Aggregate Concrete (LWAC) with improved structural performance that is made from recycled materials, such as sintered flyash aggregate, and LWAC structures that are more resistant to impact loads and other dynamic forces. Methods: The sintered flyash aggregates are added as coarse aggregate to the concrete and basalt fiber (0.25% of mix) is used as a secondary reinforcement to improve the energy absorption, impact resistance and toughness behaviour. M30 grade of concrete was arrived after laboratory trials after which the mechanical properties were evaluated. The effect of drop impact load on slabs of size 300mm x 300mm x 50mm reinforced with two layers of bundled wire mesh was studied. The flexural properties of concrete reinforced with fiber prism of size 500mm x 100mm x 100mm were evaluated. Findings: With the addition of fiber, flexural toughness index and post-cracking toughness were increased notably on the initial deflections and cracks. The conventional fiber reinforced concrete exhibited a superior peak load capacity compared to normal weight concrete, with a measured increase of 7.5%. Conversely, normal-weight concrete demonstrated a significantly higher deflection under load, exceeding that of fiber reinforced concrete by 47%. LWAC displayed a distinct increase in both peak load (18.7%) and deflection (39.13%) when compared to Normal Weight Aggregate Concrete (NWAC). The incorporation of basalt fiber enhanced the energy absorption by 150% in NWAC and 80% in LWAC. Novelty: The incorporation of fiber into lightweight concrete reduces the brittle nature of failure. The post-cracking toughness behaviour was enhanced because of the effect of crack-arresting by fibers. After the first break, it was discovered to retain residual strength, and removing the fibers from the matrix required more force. Keywords: Sintered flyash aggregate, Light weight concrete, Basalt fiber, Toughness, Impact load, Energy absorption

Seismic performance of precast lightweight aggregate concrete shear walls with supplementary V-ties

This study examined the flexural behavior of a precast lightweight aggregate concrete shear wall (PLCSW). To minimize crosstie arrangement congestion in the boundary elements and improve ductility, the conventional reinforcing crosstie was replaced with the supplementary V-tie developed by Yang et al. Additionally, a bolting technique, which combines steel plates, bolts, and nuts, was applied to the PLCSW wall-to-base connection. The behavior of these specimens was compared with the flexural behavior of conventional precast concrete shear walls (PCSW) connected via the spliced sleeve technique. Eight PCSW specimens with different crossties (supplementary V-ties or conventional reinforcing crossties) were prepared and wall-to-base connection techniques (bolting or spliced sleeve connections) applied. All specimens were tested under constant axial load and cyclic lateral loads. The ductility performance of PCSW was verified through a comparative analysis of the displacement ductility ratio and work damage index between the PCSW with supplementary V-ties and those with conventional reinforcing crossties. The ductility performance of PCSW utilizing supplementary V-ties and the bolting technique exhibited superior ductile performance resulting in a high work damage index, which was 1.22 times higher than that of the PCSW with conventional reinforcing crossties. Meanwhile, even though the shear wall specimens connected via the spliced sleeve technique were produced with normal-weight aggregate concrete, their work damage indices were slightly lower than those of the specimens utilizing conventional reinforcing crossties and the bolting technique. Consequently, the PCSWs with the spliced sleeve did not satisfy the seismic connection performance requirements specified in NEHRP, whereas the precast sand-lightweight aggregate concrete shear walls with supplementary V-ties utilizing the bolting technique satisfied the requirements. Therefore, the ductility and seismic connection performances of PCSWs with a complex detail arrangement of the boundary element can be effectively improved by using a supplementary V-tie and applying bolting techniques.

Estimating the permeability of porous aggregate concretes using electrical resistivity based tests

The established relationships between concrete's electrical resistivity and permeation properties are not applicable and might differ when porous aggregates are used. In this study, the relationships of electrical resistivity with the permeation properties of lightweight aggregate concrete (LWAC) and normal weight aggregate concrete (NWAC) were determined and compared to the permeation properties of recycled aggregate concrete (RAC). Differences in the regression slope of the three concrete types were found. At the same electrical resistivity, RAC has higher chloride permeability than LWAC and NWAC. But at the same formation factor, LWAC has higher water permeability than RAC and NWAC.

Predicting stress-strain behavior of normal weight and lightweight aggregate concrete exposed to high temperature using LSTM recurrent neural network

Lightweight aggregate is commonly used to reduce the self-weight of concrete elements which can efficiently mitigate the environmental impact. This study investigates the mechanical performance of normal weight aggregate concrete (NWAC) and Lightweight aggregate concrete (LWAC) exposed to high temperature, focusing on developing a predictive model for the stress-strain relationship of the LWAC based on the property of cement, silica fume, light weight aggregate and water/cement ratio. Mechanical properties of 30 different mixtures, including uniaxial compressive stress–strain relationship, compressive strength, modulus of elasticity, and failure strain are determined before and after high temperature exposures at 250, 500, and 750 °C. Results show that the modulus of elasticity and compressive strength of LWAC increased with exposure temperature. In particular, mixture S4 was found to outperform other mixtures, which retained 96, 75, and 46 % of compressive strength following exposures to 250, 500, and 750 °C, respectively. At all the temperatures investigated, the specimens of this mixture were able to achieve satisfactory modulus of elasticity and maximum strain. The specimens prepared with mixtures containing 75 % LECA (S23) showed a higher retention compressive strength at 750 °C. This study also utilizes the long short-term memory (LSTM) neural network to predict the stress-strain relationship of NWAC and LWAC mixtures after exposure to high temperatures. The results show that the LSTM model could adequately predict the stress-strain relationship of both LWAC and NWAC mixtures in terms of compressive strength, modulus of elasticity, and failure strain at elevated temperatures.

Comparison of lightweight and normal-weight aggregate concrete

In this experimental study, lightweight aggregate concrete (LWAC) and normal-weight aggregate concrete (NWAC) were compared within the contexts of the size of calcium hydroxide (CH) crystals in interfacial transition zone (ITZ), compressive strength, and oven-dry density. Six LWAC and NWAC mixtures were prepared for this study. Thirty-six images obtained from Scanning Electron Microscope (SEM) were used to determine the size of CH crystals in ITZ of LWAC and NWAC. Eighteen test specimens (three for each of the six LWAC and NWAC mixtures) were prepared in 150x300 mm sizes and in the form of cylinders for the compressive strength tests and also eighteen test specimens in 100x100x100 mm sizes and in the form of cubes for the oven-dry density tests. It was determined that the size of CH crystals in ITZ of LWAC is 8.43% less than (on average), compressive strength of LWAC is 39.09% more than (on average), and oven-dry density of LWAC is 10.97% less than (on average) the NWAC’s that has the same volumetric proportions of ingredients. The findings of this study show that lightweight aggregate that has high particle density, angular shape, rough surface texture, and a structure that enables chemical reaction with CH crystals will be beneficial for the ITZ microstructure and properties of concrete. It is considered that these properties should be taken into consideration in the selection of lightweight aggregate for structural concrete production.

Influence of Unidirectional Cyclic Loading on Bond between Steel Bars Embedded in Lightweight Aggregate Concrete

The topic of present research is the experimental investigation of pull-out resistance of B500B-type ribbed reinforcing steel bars embedded in lightweight aggregate concrete (LWAC) under unidirectional cyclic loading. Only a limited amount of standardized data on bond strengths are available in the case of cyclic loading, especially for lightweight aggregate concrete. This paper deals with the experimental comparison of bond behavior of steel bars embedded in LWAC with expanded clay (Liapor) aggregate and normal weight aggregate concrete (NWAC) specimens by means of standard (non-cyclic) and cyclic pull-out tests. The LWAC and NWAC specimen’s mixes were identical except for the type of the coarse aggregate. It was found that the bond strength determined by non-cyclic pull-out tests showed a higher standard deviation compared to that for compression and splitting tensile strength tests. The shape of the characteristic bond strength–the slip curve was similar in the case of LWAC and NWAC and the failure mode was the same for both types of aggregate. Moreover, the maximum value of bond stress was identical for LWAC and NWAC and also no significant difference was found in the low cycle number fatigue. Both mixes were able to resist the maximum pull-out force multiple times in the case of cyclic loading because there was no time for the development of cracks.

Technical Assessment of Green lightweight concrete containing manufactured plastic aggregates

The disposal of plastic waste is a global problem and many solutions have already been proposed to lower the environmental impact. The utilization of manufactured plastic-based coarse aggregate in concrete is one of the possible alternatives. The current study focuses on evaluating the fresh and hardened properties of concrete incorporating the plastic based manufactured aggregates. The concrete mixes were prepared at a constant water to cement ratio of 0.5 and four replacement levels (25%, 50%, 75% and 100%) of manufactured plastic-based aggregates along with two references mixes (Normal aggregate concrete and Lightweight aggregate concrete). The slump increased, while the fresh density, compressive strength and splitting tensile strength of manufactured aggregate concrete decreased with increased in the replacement ratio of manufactured aggregates. The percentage decrease for dry density, compressive strength and splitting tensile strength at 100% replacement of coarse aggregate in comparison to normal weight aggregate concrete was found to be 18.6%, 28% and 37% respectively. The Poisson ratio and abrasion values increased with increase in the replacement percentage. In addition, to predict the splitting tensile strength of concrete containing plastic-based aggregate, an equation was also proposed. Overall, the manufactured aggregates have displayed their ability to be used for construction purposes specifically where lightweight structural concrete is required as majority of properties satisfied the ASTMC330/C330M − 14 criteria.

최소 인장 철근비로 배근된 경량골재 콘크리트 T형 보의 휨 거동

이 연구의 목적은 KCI 2017 설계기준에서 제시하는 최소 인장 철근비(PSUBs,min/SUB)로 배근된 경량골재 콘크리트(lightweight aggregate concrete, LWAC) T형 보의 휨 거동을 평가하고 보통중량 콘크리트(normal-weight aggregate concrete, NWC) 보와 동등한 연성 확보 측면에서 LWAC 보의 최소 인장 철근비(PSUBs,min/SUB)의 보정계수(χ₁)를 제시하는 것이다. 보의 휨 연성은 4개의 T형 단순보휨 실험 및 2차원 비선형으로부터 평가하였다. LWAC T형 보의 변위연성비(µSUBΔ/SUB)는 인장 철근비(PSUBs/SUB)가 감소할 때 증가하는 경향을 보였으나, PSUBs,min/SUB 수준으로 감소할 때에는 µSUBΔ/SUB가 오히려 감소하였는데, 이 특성은 콘크리트 단위용적중량(ωSUBc/SUB)이 낮을수록 더 현저하였다. 따라서 비선형해석을 이용한 변수연구로부터 LWAC의 PSUBs,min/SUB에 대한 χ₁는 ωSUBc/SUB의 함수로 제시될 수 있었다. 결과적으로 LWAC 보의 PSUBs,min/SUB는 동일한 조건의 NWC 보의 연성과 동등한 수준 측면에서 ωSUBc/SUB의 감소와 함께 증가시킬 필요가 있다.

Effect of Mineral Admixture, W/B Ratio and Elevated Temperature on Strength of Lightweight Expanded Clay Aggregate Concrete

Abstract: The present paper focused on development ofstructural lightweight concrete by using light weight expandedclay aggregate (LECA) with unit weight of 1700 kg/m3 to 1900kg/m3 and compressive strength of 40 MPa. In this study,investigation was done using LECA as coarse aggregate inconcrete by replacing normal aggregate in three differingvolume fractions i.e., 30%, 40% and 50% with different w/bratios 0.40, 0.50 and 0.60 to produce lightweight expanded clayaggregate concrete (LECAC) with addition of chemicaladmixture. For that, concrete mix design was done using ISmethod and replacement of lightweight aggregate wascalculated based on volume batching. The effect of mineraladmixture (i.e., 10% microsilica) on the properties oflightweight expanded clay aggregate concrete and normalweight aggregate concrete such as workability of freshconcrete, compressive strength and flexural strength ofconcrete were compared. The studies also include the effect ofelevated temperature on light weight expanded clay aggregateconcrete and normal weight aggregate concrete.Index Terms: Normal weight aggregate concrete (NWAC),Light weight expanded clay aggregate (LECA). Light weightexpanded clay aggregate concrete (LECAC), Elevatedtemperature.

The strength of lightweight aggregate in concrete – A Review

Concrete elements are the heaviest weight in structure, and it is the main component of the dead load in structure. Lightweight concrete is used to minimize overall dead load in structures, and also has a remarkable fire resistance quality more than normal weight aggregate concrete. Lightweight concrete can be characterized as a concrete consists of normal and artificial lightweight aggregate such as lightweight expanded clay aggregate (LECA). LECA produced in a rotary kiln which is approximately 50% lighter than normal aggregate, which is a new method in minimizing concrete self-weight. The main purpose of concrete in structure is to resist the compression stresses, the tests need to prove the effectiveness of using LECA in concrete to produce acceptable compression strength. For this reason, many attempts has been made to discuss and review the strength of structural element using LECA. This paper reviews several tests for the strength of LECA concrete by determining the mechanical properties such as flexural strength and compressive strength. The LECA concrete compressive strength is found to be slightly lower than normal weight aggregate concrete. It can be seen from researches results that LECA concrete produced medium strengths, both in compressive and flexural.

Stress-strain relationship for plain and fibre-reinforced lightweight aggregate concrete

Lightweight aggregate concrete (LWAC) shows good performance in structural applications owing to its expected lower contribution to the deadweight of a structure, it nonetheless exhibits significant reduction in certain mechanical properties compared with the normal weight aggregate concrete. The inclusion of fibres could provide some positive changes to its mechanical properties and stress–strain behaviour. This study experimentally investigated the mechanical properties and full stress–strain curve of LWAC reinforced with steel and carbon fibres, involving specimens of strength classes ranging from LC40 to LC60 and fibre volume fractions from 0% to 0.9%. The test results showed that steel fibres could significantly improve the flexural strength and splitting tensile strength. Both the steel and carbon fibres strengthened the crack resistance of LWAC, while the compressive strength was not obviously enhanced. A general stress–strain model adapted to both plain LWAC and fibre-reinforced LWAC was proposed by comparing and modifying the existing models, and a statistically stochastic damage constitutive model was derived. The validity of the proposed models was examined by experimental results and test data from other studies.

The Structural Characteristics of Lightweight Aggregate Concrete Beams

This paper aims to investigate the structural behavior of reinforced lightweight concrete beams. Attapulgite aggregate and crushed clay brick aggregate were used as coarse lightweight aggregate to produce structural lightweight aggregate concrete with 25 Mpa and 43.6 Mpa cube compressive strength and 1805 Kg/m3 and 1977 Kg/m3 oven dry density respectively. The result of reinforced lightweight concrete beams compared with reinforced normal weight concrete beams, which have 50.5 Mpa cylinder compressive strength and 2317 Kg/m3 oven dry density. For each type of concrete two reinforced concrete beams with (1200 mm length × 180 mm height × 140 mm width), one of them tested under symmetrical two-points load STPL (a/d = 2.2) and another one tested under one-point load OPL (a/d=3.3) at 28 days. The experimental program shows that a structural lightweight aggregate concrete can be produced by using Attapulgite aggregate with 25 MPa cube compressive strength and 1805 Kg/m3 oven dry density and by using crushed clay brick aggregate with 43.6 MPa cube compressive strength and 1977 Kg/m3 oven dry density. The weight of Attapulgite aggregate concrete and crushed clay bricks aggregate concrete beam specimens were lower than normal weight aggregate concrete beams by about 20.56% and 13.65% respectively at 28 days. As for the ultimate load capacities of beam specimens, the ultimate load of Attapulgite aggregate concrete beams tested under STPL were lower than that of crushed clay bricks aggregate concrete beams and normal weight aggregate concrete beams by about 4.85% and 5% respectively. While the ultimate load capacities of reinforced Attapulgite concrete beams tested under OPL were lower than that of reinforced crushed clay bricks aggregate concrete beams and reinforced normal weight aggregate concrete beams by about 10.3% and 10.5% respectively. Finally, Attapulgite aggregate concrete and crushed clay bricks aggregate concrete showed ductility and toughness less than that of Normal weight aggregate concrete.

Effects of Aggregate Types on the Stress-Strain Behavior of Fiber Reinforced Polymer (FRP)-Confined Lightweight Concrete.

The realization of reducing concrete self-weight is mainly to replace ordinary aggregates with lightweight aggregates; such replacement usually comes with some intrinsic disadvantages in concrete, such as high brittleness and lower mechanical properties. However, these shortages can be effectively remedied by external confinement such as fiber reinforced polymer (FRP) jacketing. To accurately predict the stress-strain behavior of lightweight concrete with lateral confinement, it is necessary to properly understand the coupling effects that are caused by diverse aggregates types and confinement level. In this study, FRP-confined lightweight concrete cylinder with varying aggregate types were tested under axial compression. Strain gauges and linear variable displacement transducers were used for monitoring the lateral and axial deformation of specimens during the tests. By sensing the strain and deformation data for the specimens under the tri-axial loads, the results showed that the lateral to axial strain relation is highly related to the aggregate types and confinement level. In addition, when compared with FRP-confined normal weight aggregate concrete, the efficiency of FRP confinement for lightweight concrete is gradually reduced with the increase of external pressure. Replace ordinary fine aggregate by its lightweight counterparts can be significantly improved the deformation capacity of FRP-confined lightweight concrete, meanwhile does not lead to the reduction of compressive strength. Plus, this paper modified a well-established stress-strain model for an FRP-confined lightweight concrete column, involving the effect of aggregate types. More accurate expressions pertaining to the deformation capacity and the stress-strain relation were proposed with reasonable accuracy.

Mechanical, durability and microstructure properties of lightweight concrete using aggregate made from lime-treated sewage sludge and palm oil fuel ash

This paper reports the investigation on toxicity characteristics, microstructure, physical and mechanical properties of artificial Posslite lightweight aggregate (LWA) made from lime-treated sewage sludge (SS) and palm oil fuel ash (POFA). The presence of crystals and a dense shell of Posslite LWA enhanced its strength and the rounded shape of LWA enhanced the workability of fresh lightweight aggregate concrete (LWAC). Results showed that mechanical and durability properties of Posslite LWAC were comparable to normal weight aggregate concrete (NWAC). Posslite LWAC possesses compressive strength, VPV, sorptivity, chloride diffusion of 50.4 MPa, 8.7%, 0.0151 mm/s0.5 and 2.12 × 10−11 m2/s, respectively.

Experimental Evaluation of Thermal Performance and Durability of Thermally-Enhanced Concretes

The thermal performance and durability of the thermally-enhanced concrete with various insulating materials were evaluated through a series of tests. Three types of insulating materials—diatomite powder, hollow micro-spheres, and a micro-foam agent—were used for both normalweight aggregate concrete (NWAC) and lightweight aggregate concrete (LWAC). The thermal conductivity was measured by two different test methods: quick thermal conductivity meter (QTM) and guarded hot wire (GHW) methods. Then, the results were compared with each other. All insulating materials used in this study proved their ability to reduce the thermal conductivity. Additionally, it can be found that the trend of a decrease in air-dry density is similar to that of thermal conductivity of thermally-enhanced concrete. Additional thermal transmission tests with seven large-scale specimens were conducted by using the calibrated hot box (CHB). However, from this tests, it was seen that thermal transmission reduction for tested specimens were not large compared to the thermal conductivity reduction measured by QTM and GHW, due to multiple heat transfer. To examine the durability of thermally-enhanced concretes, accelerated carbonation and freeze-thaw cycle tests were conducted. From the results, it can be found that the thermally-enhanced concrete shows good freeze-thaw resistance. However, the carbonation rates of the concretes increased rapidly and additional methods to improve the carbonation resistance should be considered.

A study of the durability of recycled green building materials in lightweight aggregate concrete

In this study, waste tire powder and waste liquid crystal display (LCD) glass sand are used as recycled materials. With a fixed water to binder ratio (W/B=0.4), the use of fly ash and slag as cement-replacement materials. waste tire powder and waste LCD glass sand, which passed the sieve screen size # 30(0.595mm), were used to replace fine aggregates at 0%, 5% and 10% in producing lightweight aggregate concrete. The fresh property test was processed in accordance with ACI concrete mix proportion design. Harden and durability tests were performed at 7, 28, 56 and 91days. The results showed that the slump increased or decreased with the addition of different types of recycled materials, but still met the design slump of 150–180mm. Concrete workability and the unit weight decreased after adding rubber powder to concrete. As the replacement rates of waste glass sand and waste rubber powder increase, the compressive strength tends to decrease. At 56days, the ultrasonic wave velocity of normal concrete was higher than lightweight aggregate concrete; the lightweight aggregate concrete with 10% glass sand provided the highest ultrasonic wave velocity of the lightweight aggregate concretes. Sulfate resistance tests showed that the normal weight aggregate concrete was better than the lightweight aggregate. Mixing two kinds of recycled materials also resulted in better resistance. Studies showed that adding an appropriate amount of recycled materials might improve the durability of lightweight aggregate concrete.

Development of structural–functional integrated concrete with macro-encapsulated PCM for thermal energy storage

Abstract In this research, we prepared macro-encapsulated paraffin-lightweight aggregate (LWA) for the development of structural–functional integrated normal weight aggregate concrete (NWAC). The macro-encapsulated paraffin–LWA was prepared by incorporation of paraffin into porous LWAs through vacuum impregnation. The sealing performance of the epoxy was evaluated by thermal cycling test while the thermal conductivity of macro encapsulated Paraffin–LWAs was improved by incorporating different percentages of graphite powder into epoxy. The chemical compatibility, thermal properties, thermal stability and reliability of macro-encapsulated paraffin–LWA was also determined. Finally, the compressive strength and thermal performance of concrete containing macro-encapsulated paraffin–LWA was evaluated. Test results showed that the maximum percentage of paraffin absorbed by LWA was 70%. The thermal conductivity of the macro-encapsulated paraffin–LWA with 15% graphite powder was 162% higher than that of epoxy. Moreover, the developed macro-encapsulated paraffin–LWA was found to be chemically compatible, thermally stable and reliable (did not show any sign of degradation below 150 °C and sustained 1000 cycles of melting and freezing) and it has high latent heat storage capacity (102.5 J/g). The compressive strength of NWAC with macro-encapsulated PCM-LWA at 28 days ranged from 33.29 to 53.11 MPa, therefore presenting an opportunity for structural applications. The indoor thermal performance test revealed that NWAC with macro-encapsulated paraffin–LWA can function in reducing the energy consumption by decreasing the indoor temperature and shifting the loads away from the peak periods. Thus, we demonstrated and produced concrete with structural and thermostatic properties.

Experimental study on creep and shrinkage of high-performance ultra lightweight cement composite of 60MPa

Creep and shrinkage behaviour of an ultra lightweight cement composite (ULCC) up to 450 days was evaluated in comparison with those of a normal weight aggregate concrete (NWAC) and a lightweight aggregate concrete (LWAC) with similar 28-day compressive strength. The ULCC is characterized by low density < 1500 kg/m 3 and high compressive strength about 60 MPa. Autogenous shrinkage increased rapidly in the ULCC at early-age and almost 95% occurred prior to the start of creep test at 28 days. Hence, majority of shrinkage of the ULCC during creep test was drying shrinkage. Total shrinkage of the ULCC during the 450-day creep test was the lowest compared to the NWAC and LWAC. However, corresponding total creep in the ULCC was the highest with high proportion attributed to basic creep (≥ ~90%) and limited drying creep. The high creep of the ULCC is likely due to its low elastic modulus. Specific creep of the ULCC was similar to that of the NWAC, but more than 80% higher than the LWAC. Creep coefficient of the ULCC was about 47% lower than that of the NWAC but about 18% higher than that of the LWAC. Among five creep models evaluated which tend to over-estimate the creep coefficient of the ULCC, EC2 model gives acceptable prediction within +25% deviations. The EC2 model may be used as a first approximate for the creep of ULCC in the designs of steel-concrete composites or sandwich structures in the absence of other relevant creep data.

Evaluation method of cracking resistance of lightweight aggregate concrete

The cracking behavior of lightweight aggregate concrete (LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete (NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.