Self-compacting Lightweight 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.

The influence of nanosunflower ash and nanowalnut shell ash on sustainable lightweight self-compacting concrete characteristics

The absence of biodegradability exhibited by plastics is a matter of significant concern among environmentalists and scientists on a global scale. Therefore, it is essential to figure out potential pathways for the use of recycled plastics. The prospective applications of its utilisation in concrete are noteworthy. The use of recycled plastic into concrete, either as a partial or complete substitution for natural aggregates, addresses the issue of its proper disposal besides contributing to the preservation of natural aggregate resources. Furthermore, the use of agricultural wastes has been regarded as a very promising waste-based substance in the industry of concrete manufacturing, with the aim of fostering the creation of an environmentally sustainable construction material. This paper illustrates the impact of nano sunflower ash (NSFA) and nano walnut shells ash (NWSA) on durability (compressive strength and density after exposure to 800 °C and sulphate attack), mechanical properties (flexural, splitting tensile and compressive strength) and fresh characteristics (slump flow diameter, T50, V-funnel flow time, L-box height ratio, segregation resistance and density) of lightweight self-compacting concrete (LWSCC). The waste walnut shells and local Iraqi sunflower were calcinated at 700 ± 50 °C for 2 h and milled for 3 h using ball milling for producing NSFA and NWSA. The ball milling succeeded in reducing the particle size lower than 75 nm for NSFA and NWSA. The preparation of seven LWSCC concrete mixes was carried out to obtain a control mix, three mixtures were created using 10%, 20% and 30% NWSA, and the other three mixtures included 10%, 20% and 30% NSFA. The normal weight coarse aggregates were substituted by the plastic waste lightweight coarse aggregate with a ratio of 75%. The fresh LWSCC passing capacity, segregation resistance, and filling capability were evaluated. The hardened characteristics of LWSCC were evaluated by determining the flexural and splitting tensile strength at 7, 14 and 28 days and the compressive strength was measured at 7, 14, 28 and 60 days. Dry density and compressive strength were measured after exposing mixes to a temperature of 800 °C for 3 h and immersed in 10% magnesium sulphate attack. The results demonstrated that the LWSCC mechanical characteristics were reduced when the percentages of NWSA and NSFA increased, except for 10% NWSA substitution ratio which had an increase in splitting tensile strength test and similar flexural strength test to the control mixture. A minor change in mechanical characteristics was observed within the results of LWSCC dry density and compressive strength incorporating various NSFA and NWSA` contents after exposing to temperature 800 °C and immersed in 10% magnesium sulphate attack. Furthermore, according to the findings, it is possible to use a combination of materials consisting of 10–20% NSFA and 10–20% NWSA to produce LWSCC.

Investigating Some Properties of Hybrid Fiber Reinforced LECA Lightweight Self-Compacting Concrete

. The primary goal of this investigation is to study the effect of using mono and hybrid fibers on the fresh and hardened characteristics of Lightweight Self-Compacting Concrete (LWSCC). Slump flow test, L-box test, sieve segregation test, and V-funnel test were used to evaluate the workability of LWSCC. The mechanical characteristics of LWSCC were assessed by using compressive strength, splitting strength, and flexural strength. Four mixtures using two types of fiber: Steel fiber (St) and polypropylene fiber (PP) (0% fiber, 1% (St), 0.75% (St) +0.25% (PP), 0.5% (St) +0.5% (PP)) were made. According to the results, (St) fiber and hybrid fiber addition to LWSCC reduced its workability, although the values of tests were still within the acceptable range stander of EFNARC. The findings indicated a decrease in the values of slump flow and L-box test by adding mono and hybrid fibers to the LWSCC mixture. While the T500mm and V_ funnel tests increased by adding mono and hybrid fibers to LWSCC mixture. The results also indicate that the utilisation of (St) fiber and hybrid fibers had a significant effect on the mechanical characteristics of LWSCC. Where the flexural and splitting strengths significantly increase with the addition of (St) and hybrid fibers to the LWSCC mix.

Effect of sand fineness modulus on SCC and SCLC properties

Due to the advantageous characteristics of self-compacting concrete (SCC) and self-compacting lightweight concrete (SCLC), the advancement of the SCC is considered a remarkable engineering feat. Fine aggregate is one of the main parameters of SCC; however, its effect on SCC and SCLC properties is somewhat restricted due to the limited extent of in-depth research conducted in this field. To investigate the effect of changes in sand fineness modulus (FM) on the fresh and hardened properties of SCC and SCLC, an experimental investigation with twelve mixtures was designed. Two series of mixtures were used, each with two coarse aggregate types: Light Expanded Clay Aggregate (LECA) and natural gravel. Each series included different sand FM (2.3, 2.7, and 3.1), with the incorporation of 7% micro-silica (MS) as a cement substitute in some designs. The fresh properties of the concrete were evaluated through tests such as Slump Flow, V-Funnel, U-box, L-Box, and J-Ring, in addition to the Static Segregation Column test. For evaluating the hardened properties, 192 specimens were tested, including compressive, tensile, and flexural specimens. Moreover, fracture energy was also investigated. As the sand FM increased, it was expected that the fresh properties of concrete might decrease due to coarser aggregate volume, and the hardened properties would improve under these conditions. However, the results showed that increasing the sand FM improved the fresh and hardened properties of SCC and SCLC. By increasing the sand FM, the flowability, filling ability, and passing ability of both concrete improved, but on the other hand, elevating the sand FM reduced the segregation resistance of the mixes. In contrast, the hardened properties exhibited contrasting outcomes with increasing the sand FM. Increasing the sand FM improved the compressive strength by about 20% in both concrete types.

Evaluation and optimization of volume fraction and aspect ratio of Polyethylene Terephthalate (PET) fibers in self-compacting lightweight concrete

ABSTRACT Use of Polyethylene Terephthalate (PET) fibers to reinforce the performance of self-compacting lightweight concrete (SCLC) is reported. Evaluation and optimization of the fiber addition is based on different properties. SCLC mixes were designed using three volume fractions Vf (0.5%, 0.75% and 1%) and three aspect ratios (l/d = 15, 30 and 45) of fibers. Slump flow, T500, L-box, segregation, density, absorption, porosity, compressive, splitting tensile and flexural strengths, modulus of elasticity, ultrasonic pulse velocity, thermal conductivity, flexural toughness, and impact resistance tests were performed and evaluated statistically. The results indicated that PET fibers in fresh SCLC negatively affected the flowability and passing ability, while they improved the segregation resistance. Compressive strength and modulus of elasticity slightly increased, whereas the tensile strength was significantly improved. Substantial improvements in flexural toughness, thermal and impact resistances were recorded, indicating beneficial enhancement in toughness and ductility. Less desirably, SCLC with PET showed slight increases in absorption and porosity. The statistical analysis showed that the fiber Vf controlled majority of the tested properties rather than the aspect ratio. Based on desirability function and multi-objective optimization, the optimum Vf and l/d were 0.65% and 35.6, respectively. Theoretical obtained values were verified experimentally for all properties with 0 to ±5% variance.

Investigation of the Flexural Behavior of Bacterial Concrete Beams

Abstract Bacterial self-healing concrete is an eco-friendly and superior treatment technique that has efficient bonding capacity and compatibility with concrete compositions. It is capable of filling deep microcracks and healing the crack autonomously by calcium carbonate precipitating phenomenon which results in sustainable construction materials. The purpose of this research is to investigate the use of microorganisms Bacillus Subtilis to improve the mechanical properties and the efficiency of self-healing of reinforced concrete beams for two types of concrete, reactive powder concrete (RPC), and lightweight self-compacting concrete (LWASCC), by two methods of addition (direct addition, and encapsulation). The experimental program consists of casting six simply supported beams tested under monotonic and repeated loading. Incorporate bacteria and the precursor (calcium lactate) in concrete mixtures show an improvement in compressive strength, splitting, and flexural strength by up to 21.74 %, 10.92 %, 21.21 % by encapsulation method, and 17.7 %, 18.0 %, 20.84 % by direct addition. In addition, there is an enhancement in the first crack load and ultimate load. Microscopical image demonstrated that calcium carbonates had been deposited in the crack up to 1.0 mm width by bacterial activity within 32 days.

Shear performance of lightweight SCC composite beam internally reinforced with CFRP laminate stirrups and GFRP bars: Experimental and analytical study

This research demonstrates the structure feasibility of using carbon fiber reinforced polymer (CFRP) laminate stirrups as a form of transverse reinforcement in shear deficient GFRP reinforced lightweight self-compacting concrete (LWSCC) beams. An experimental study performed on eight full-scale shear deficient beam specimens. One beam served as the reference specimen and remaining beam specimens were internally reinforced with impregnated CFRP laminate stirrups. The parameters investigated in this study were the stirrup configuration, number of layers, stirrup spacing and width. Specimen tested under two-point loading and all results in term of load-deflection response as well as their failure modes were reported. All tested specimens failed due to shear compression failure mode along with the rupture of CFRP laminate stirrups, and the inclusion of CFRP laminate stirrups has significantly enhanced the nominal capacity of LWSCC beams ranged from 91%− 200% over control specimen. Shear strengths of the tested specimens were also theoretically predicted using different design standards. Comparison between the experimental and predicted shear strength has shown that ACI 440.1R-15, CSA S806–12, and CSA S6–14 provided the closest prediction. Therefore, it has been concluded that CFRP laminate stirrups can be used as a transverse reinforcement in GFRP reinforced LWSCC beams.

Conditions for the Preparation of Self-Compacting Lightweight Concrete with Hollow Microspheres

Producing self-compacting concrete with lightweight aggregates is a difficult task. Mixtures with a high content of expanded aggregate tend to separate. It is possible to evaluate the possibility of producing self-compacting lightweight concrete with low average density. This work presents the results of a study of self-compacting lightweight concrete on hollow microspheres. The ability of a lightweight concrete mixture on hollow microspheres with low density (ρ = 1450 ± 25 kg/m3) to self-compact has been established. The closeness in the values of the spreading diameter before and after shaking on the table Dsp,1 → Dsp,2 confirms this. The dependences (regression equations) of mobility, coefficients of the Ostwald–Weil equation, and density and strength on the W/C ratio and plasticizer concentration for lightweight concrete with a volume content of hollow microspheres of 46.4% have been established. The limits for homogeneity of lightweight concrete mixtures on hollow microspheres are W/C ≤ 0.6 and CPl ≤ 1.0%. The dispersion of quartz sand (varying the Sp/Sf ratio) in an amount of 8.7% in the composition of lightweight concrete does not have a significant effect on the self-compaction criterion and physical and mechanical properties. Changes in the physical and mechanical properties of lightweight concrete on hollow microspheres in the selected range of varying the W/C ratio and plasticizer concentration are in the following ranges: ρ = 1403–1485 kg/m3, Rfl = 3.34–5.90 MPa, Rcom = 29.6–45.7 MPa. The presence of delamination at W/C ≥ 0.6 does not allow one to correctly establish the influence of variable factors.

Shear strengthening performance of fiber reinforced lightweight SCC beams

In recent years, the demand for fiber reinforced lightweight concrete (FLWC) has increased rapidly to make high-strength, durable and lightweight structures. The strengthening behaviour of FLWC has never been studied in the literature and currently there are no standard guidelines for strengthened FLWC beams. Therefore, the main aim and objective of the current experimental study is to investigate the shear behaviour of fiber reinforced lightweight self-compacting concrete (FLWSCC) beams externally strengthened with CFRP strips. Six full-scale reinforced concrete (RC) beams were tested under four-point bending with varying CFRP strip spacing, number of layers, and configuration. One additional beam served as the control specimen to compare the performance of the strengthened specimens. The experimental results indicated that the external CFRP strips enhanced the strength and stiffness of the strengthened FLWSCC specimens. The strength enhancement ranged from 12% to 91% and pull out of steel fiber and debonding of CFRP strips was the predominant mode of failure in the control and strengthened specimens. The presence of steel fibers in the concrete has increased the shear strength of concrete and limits the external contribution of CFRP strips. Furthermore, all the experimental results were compared with theoretically predicted shear capacities using various FRP design standards for external strengthening. All the design standards have overestimated the shear capacity of FLWSCC specimens and CNR-DT (2013) design standard was found to be the most conservative as compared to other design standards. In addition, a lightweight modification factor has been recommended for strengthened FLWSCC beams

Influence of cyclic loading on lightweight self-compacting concrete double-skin tubular columns

Self-compacting concrete (SCC) has gained prominence in recent decades due to its inherent qualities, particularly its ability to compact autonomously. SCC proves invaluable in scenarios where traditional compaction is challenging due to placement conditions or the presence of close space reinforcement. This study focuses on evaluating the structural performance of lightweight self-compacting concrete (LWSCC) columns confined with glass fiber-reinforced polymer (GFRP) and steel tube (ST) subjected to cyclic loading. The LWSCC columns, denoted as LWSTC, are designed with inner steel tubes and outer GFRP tubes, imparting corrosion resistance and reduced weight alongside enhanced ductility. Through quasi-static loading, five fabricated LWSTC columns were subjected to assess their structural response under dynamic effects. The investigation delves into three key variables: axial load ratio, reinforcement ratio, and the replacement ratio of coarse lightweight expanded clay aggregate (LECA) in the fabricated LWSTC columns. A comprehensive analysis of various parameters, including skeleton curves, ductility, hysteretic cycles, damage modes, dissipation of energy capacity, stiffness behavior, strain spreading, and strength reduction, was conducted on the LWSTC columns. The findings reveal that the replacement of LECA with natural aggregates has an insignificant impact, whereas varying the axial load ratio significantly influences the structural behavior of LWSTC. Notably, LWSTC exhibits a remarkable 121% higher horizontal load capacity compared to counterparts using natural aggregate. Furthermore, LWSTC demonstrates superior axial strength and enhanced capability for energy dissipation.

Behavior of Steel–Lightweight Self Compacting Concrete Composite Beams with Various Degrees of Shear Interaction

This study investigated the use of lightweight self-compacting concrete (LWSCC), which represents a trend in producing high-performance concrete, as slabs in steel-concrete composite beams with headed studs as shear connectors. Three push-out test specimens were fabricated and tested to assess the shear strength and behavior of M16-headed stud connectors embedded in LWSCC. Based on the push-out test results, six steel-LWSCC composite beams were manufactured and tested as simply supported composite beams. In addition, a steel-normal weight self-compacting concrete (NWSCC) composite beam specimen with full shear interaction was manufactured and tested for comparison. The main variables taken into account in this study were the degree of shear interaction and regions of bending moment (sagging or hogging). It was observed that the increase in degree of shear interaction from 50 to 100% improved the ultimate carrying capacity, the service load, and the stiffness of the tested steel-LWSCC beam specimens by a ratio reached to 96, 95, and 122%, respectively, when subjected to sagging bending moments and by a ratio reached to 57, 59, and 134%, respectively, when subjected to hogging bending moments. In addition, it was noted that the deflection and the end slip values for steel-LWSCC specimens under a sagging bending moment are smaller than those under a hogging bending moment, which have the same degree of shear interaction and at the same load level. Moreover, the experimental results show that the ultimate carrying capacity, service load, and stiffness values for the steel-NWSCC composite beam were higher than those for the steel-LWSCC beam specimens that have the same properties, while the ultimate deflection and end slip were smaller. Doi: 10.28991/CEJ-2023-09-11-04 Full Text: PDF

Fresh, mechanical and impact properties of self-compacting lightweight concrete containing waste PET fibers

Fresh, mechanical and impact properties of self-compacting lightweight concrete containing waste PET fibers

Mechanical and shrinkage performance of steel fiber reinforced high strength self-compacting lightweight concrete

This study investigated the effects of mixture proportion on the mechanical and shrinkage behaviors of steel fiber reinforced high strength self-compacting lightweight concrete (SHSLC) mixtures incorporating bottom ash aggregates for internal curing. In this study, different types of fine aggregates, fine aggregate ratios, supplementary materials such as silica fume (SF) and colloidal nano-silica (CNS), and four types of steel fibers were considered to develop SHSLC. The self-compacting characteristics of concrete were evaluated by means of slump flow, J-ring flow, and V-funnel tests. The test results indicate that incorporation of SF and CNS had a positive effect on the mechanical properties, but 4% incorporation of CNS decreased workability and strength due to the agglomeration of mixture. The addition of steel fibers improved compressive strength, and flexural toughness of SHSLC, but reduced the flowability and passing ability with increased fiber contents. Due to the internal curing from coarse bottom ash, significant reduction of autogenous shrinkage up to 33% was observed, whereas 7% for drying shrinkage. The incorporation of fibers reduced the autogenous and drying shrinkage up to 31% and 22% compared with non-fiber reinforced concrete, respectively. Finally, the autogenous shrinkage behavior was simulated with several models in the literature, and a model for high strength self-compacting lightweight concrete with and without fibers considering equivalent age was proposed.

Comparative Performance of SF, PPF and Hybrid Fiber-Reinforced Self-Compacting Lightweight Concrete under Fire Exposure

Comparative Performance of SF, PPF and Hybrid Fiber-Reinforced Self-Compacting Lightweight Concrete under Fire Exposure

The Effect of Different Types of Aggregate and Additives on the Properties of Self-Compacting Lightweight Concrete

The major aim of this research is study the effect of the type of lightweight aggregate (Porcelinite and Thermostone), type and ratio of the pozzolanic material(SF and HRM) and the use of different ratios of w/cm ratio(0.32 and 0.35) on the properties of SCLWC in the fresh and hardened state. SF and HRM are used in three percentage 5%,10%, and 15% as a partial replacement by weight of cement for all types of SCLWC. The requirements of self-compatibility for SCC are fulfilled by using the high performance superplasticizer (G51) at 1.2liter per 100 kg of cement. The values of air dry density and compressive strength at age of 28 days within the limits of structural lightweight concrete. The air dry density and compressive strength at age of 28 days for w/cm ratio(0.32) for SCLWC of Porcelinit aggregate are 1964 kg/m3 and 29.57 MPa, respectively. The corresponding values for the SCLWC of Thermostone aggregate are 1820 kg/m3 and 25.75 MPa, respectively. The results show that the HRM performance which is locally available is better than SF in production of SCLWC.

Assessing the performance of palm oil fuel ash and Lytag on the development of ultra-high-performance self-compacting lightweight concrete with waste tire steel fibers

Recent advances in ultra-high-performance concrete (UHPC) materials have emphasized the necessity for continuous research. This imperative is particularly pronounced given the widespread demand for materials that facilitate the design and construction of long-span bridges, high-rise towers, and architecturally complex structures. The current study strives to address this need by developing a novel ultra-high-performance self-compacting lightweight concrete (UHPSCLWC). This research introduced Palm Oil Fuel Ash (POFA) and Lytag as replacements for specific conventional components. Specifically, 5%–25% POFA was utilized at 5% intervals as a partial substitute for cement to counter the heavy cement requirement typical of UHPC. Similarly, 5%–25% Lytag was used in 5% increments as a lightweight aggregate substitute for fine aggregate. To further optimize UHPC's production cost, waste tire steel fibers (WTSF) sourced from discarded truck tires were employed as primary reinforcement. This study comprehensively evaluates the rheological, physical, functional, and extreme durability properties of the UHPSCLWC and provides microstructural analysis. Test results suggest that samples utilizing 20% POFA and Lytag demonstrate optimal improvements across assessed characteristics, notably improved thermal and acoustic performance. At 90 days, the highest enhancement in compressive strength, modulus of elasticity, and modulus of rupture was 14.09%, 33.54%, and 17.44% for samples with 20% POFA and Lytag. Due to the unique properties and porous nature of Lytag, the hardened density of UHPSCLWC was reduced from 1993 kg/m3 to 1705 kg/m3. These modified samples also displayed enhanced durability, reduced mass loss and chloride penetration, and increased residual compressive strength when subjected to extreme conditions. Furthermore, the optimal inclusion of 20% POFA and Lytag in the mixture facilitated higher peaks of hydration phases, as observed in x-ray diffraction analysis. The findings of this study suggest the practical potential of POFA and Lytag in developing an innovative UHPSCLWC modified with waste tire steel fibers. This study adds valuable insights to the growing body of knowledge in the field of UHPC material development.

Lightweight SCC Development in a Low-Carbon Cementitious System for Structural Applications.

The utilization of manufactured lightweight aggregates adds another dimension to the cost of the preparation of self-compacting concrete (SCC). The common practice of adding absorption water to the lightweight aggregates before concreting leads to inaccurate calculations of the water-to-cement ratio. Moreover, the absorption of water weakens this interfacial bond between aggregates and the cementitious matrix. A particular type of black volcanic rock with a vesicular texture known as scoria rocks (SR) is utilized. With an adapted sequence of additions, the occurrence of water absorption can be minimized to overcome the issue of calculating the true water content. In this study, the approach of preparing the cementitious paste first with adjusted rheology followed by the addition of fine and coarse SR aggregates enabled us to circumvent the need for adding absorption water to the aggregates. This step has improved the overall strength due to the enhanced bond between the aggregate and the cementitious matrix, rendering a lightweight SCC mix with a target compressive strength of 40 MPa at 28 days, which makes it appropriate for structural applications. Different mixes were prepared and optimized for the best cementitious system that achieved the goal of this study. The optimized quaternary cementitious system included silica fume, class F fly ash, and limestone dust as essential ingredients for low-carbon footprint concrete. The rheological properties and parameters of the optimized mix were tested, evaluated, and compared to a control mix prepared using normal-weight aggregates. The results showed that the optimized quaternary mix satisfied both fresh and hardened properties. Slump flow, T50, J-ring flow, and average V-funnel flow time were in the ranges of 790-800 mm, 3.78-5.67 s, 750-780 mm, and 9.17 s, respectively. Moreover, the equilibrium density was in the range of 1770-1800 kg/m3. After 28 days an average compressive strength of 42.7 MPa, a corresponding flexural load of over 2000 N, and a modulus of rupture of 6.2 MPa were obtained. The conclusion is then drawn that altering the sequence of mixing ingredients becomes a mandatory process with scoria aggregates to obtain high-quality lightweight concrete for structural applications. This process leads to a significant improvement in the precise control of the fresh and hardened properties, which was unachievable with the normal practice used with lightweight concrete.

Structural behavior of reinforced lightweight self‐compacting concrete beams using expanded polystyrene as coarse aggregate and containing polyethylene terephthalate fibers

AbstractThrough this study, an attempt was made to produce concrete beams from self‐compacting concrete (SCC) contain expanded polystyrene (EPS) beads as coarse aggregate and waste plastic fibers (WPFs) produced from cutting disposed packing straps in site. The beams were designed according to ACI‐318‐14, where three different reinforcement ratios were chosen for the purpose of checking the conductance of thresholds made of this type of environmentally friendly concrete under bending loads. The use of EPS with WPFs had a significant positive effect in reducing the density of concrete, and the highest percentage of reduction was equal to (38.46%). Using WPFs had a positive effect in increasing the flexural toughness of concrete prisms, and the maximum increment was equal to (180%) compared with these made from the reference mix. The results proved the possibility of producing lightweight concrete from the use of EPS waste and WPFs, three of which are structurally can be classified as lightweight concrete combination of normal weight and lightweight aggregates according to specifications requirements of ASTM330/330M‐14. Reinforced lightweight SCC beams behaved under flexural loads similar to the reinforced concrete beams made from normal weight concrete counterparts under flexural loads.

Experimental investigation of flexural buckling behaviour of self-compacting lightweight concrete-filled cold-formed built-up box section (CFBBS) columns

This paper presents an experimental investigation of the flexural buckling behaviour and resistance of innovative self-compacting lightweight concrete (LWSCC)-filled cold-formed built-up box section (CFBBS) columns. A series of sixteen LWSCC-filled CFBBS columns and four reference hollow columns formed by two nested asymmetric lipped channel sections using breakstem rivets at flanges with various member relative slendernesses ratios, concrete strengths and section sizes were tested under pin-ended boundary conditions. Material tests and initial global geometry imperfection measurements were carried out and reported in present study. The failure modes and deformation developments, lateral deflection distribution along the column specimens, flexural buckling resistance and load-end shortening relationship of the specimens were scrutinised and discussed concerning the effect of parameters and the associated coupling effects. Furthermore, a comprehensive strain analysis was conducted and reported based on the longitudinal and lateral strain developments at both compression and tension zones under flexure; it was found that the composite action abated as the member length increased. Finally, as there is no existing design codes for LWSCC-filled CFBBS columns, the experimental results were used to evaluate the applicability of relevant international codified provisions, including Eurocode (EC4), Australia/New Zealand Standard (AS/NZS 2327) and America Specification (AISC 360-16). It was found that AS/NZS 2327 yielded the most accurate and moderately scattered predictions while the predictions from EC4 were found to be the most scattered but with reasonable accuracy and those from AISC 360-16 were overly conservative, albeit the least scattered among these design codes.

The Influence of Nano-Silica on Some Properties of Light Weight Self-Compacting Concrete Aggregate

Lightweight concrete (LWC) has been used successfully in building constructions for many years due to its physical properties and its lightweight with high thermal insulation and durability. Recently, this work was done on a new type of concrete: lightweight self-compacting concrete (LWSCC) that combines the feature of lightweight and self-compacting concrete simultaneously. In this study, light expanded clay aggregate (LECA) was used as coarse aggregate in (LWSCC) mixtures, using nano-silica as a partial replacement of cement with three percent (0.5, 0.75, and 1%) by mass of cement. They were tested to evaluate these values of fresh characteristics through slump flow time and diameter, L-box, and segregation tests. The results of the fresh concrete tests showed a decrease in the workability of the concrete in the mixtures containing nano-silica due to the increase in fine materials in the mixture. The effects of nano-silica on the hardened properties of (LWSCC) such as compressive strength, flexural strength, splitting tensile strength, oven-dry density, and scanning electron microscopy (SEM), have improved. The mixtures containing nano-silica were investigated and compared with the reference mixture, where the results of the tests showed a significant improvement in the mechanical properties by (17.35, 16.27, 11.73, and 3.82%) for each of the compressive strength, flexural strength, splitting tensile strength and oven dry density respectively. In the presence of nano-silica, the replacement percentage of 1% recorded the best results in all tests at 90 days of curing.