Normal Weight Concrete Research Articles

Comparative life cycle assessment (LCA) of the composite prefabricated ultra-shallow slabs (PUSS) and hollow core slabs in the UK

Life cycle assessment studies of precast construction methods highlight their superiority over traditional cast-in-situ construction in reducing buildings’ environmental impacts. Among the extensively used precast structural elements, hollow core precast slabs have proven benefits with their practical implementation in flooring systems across various flooring spans and live loads. This paper presents a case study comparing the global warming potential and embodied energy impacts of a recently developed lightweight prefabricated composite flooring system (PUSS) with zinghollow core precast slabs in the UK. The analysis is based on 16 live load/flooring span scenarios, between 6 and 12m. The study examines the benefits and drawbacks of utilising different concrete types in PUSS flooring, namely normal weight concrete, lightweight aggregates concrete and geopolymer concrete. PUSS with GPC demonstrates potential savings of up to 50 % in GWP compared with hollow core slabs, while PUSS with LWC exhibits potential savings of up to 35 % in total EE compared with hollow core slabs.

Moisture Impact on Static and Dynamic Modulus of Elasticity in Structural Normal-Weight Concretes.

In the case of concrete built into a structure, the static secant modulus of elasticity (Ec,s) is often estimated based on its dynamic value (Ed) measured by the ultrasonic pulse velocity method instead of direct tests carried out on drilled cores. Meanwhile, the prevailing equations applied to estimate Ec,s often overlook the impact of concrete moisture. This study aimed to elucidate the moisture impact across two normal-weight structural concretes differing in compressive strength (51.6 and 71.4 MPa). The impact of moisture content was notably more evident only for the weaker concrete, according to dynamic modulus measurements. In other cases, contrary to the literature reports and expectations, this effect turned out to be insignificant. These observations may be explained by two factors: the relatively dense and homogeneous structure of tested concretes and reduced sensitivity of Ec,s measurements to concrete moisture condition compared to Ed measurements obtained using the ultrasonic method. Additionally, established formulas to estimate Ec,s were verified. The obtained modulus results tested under different moisture conditions of normal-weight concretes were also compared with those of lightweight aggregate concretes of identical volume compositions previously obtained in a separate study.

Performance improvement of glass-based lightweight aggregates through thermodynamic modelling design and lightweight mortar validation

To reduce environmental impact of sintered lightweight aggregates (LWAs), in this study, novel glass-based LWAs were produced from municipal solid wastes at 900 °C. The mix was designed by thermodynamic modelling to optimize the phase composition, liquid phase properties, and microstructure of the LWAs. Results demonstrated that the inclusion of incinerated sewage sludge ash (ISSA) increased the viscosity of the liquid phase, resulting in a refined pore structure characterized by smaller, more isolated pores, and thicker pore walls. Additionally, ISSA facilitated the formation of various crystalline phases (e.g. wollastonite) to stabilize the pore structure, thereby enhancing densification and matrix strength. Leaching behaviour tests confirmed the suitability of glass-based LWAs for environmentally safe lightweight products. Lightweight mortars incorporating developed LWAs exhibited a high 28-day compressive strength (up to 57.9 MPa) with a low density of 1688 kg/m3 and a low thermal conductivity of 1.0 W/(m·K). The energy simulation revealed substantial reductions in energy consumption when the lightweight mortars were utilized in the building compared with the reference building using normal-weight C30 concrete, underscoring its promising role in conserving energy and reducing carbon emissions.

Analysis of fracture mechanism and fracture energy prediction of lightweight aggregate concrete

The fracture energy of lightweight aggregate concrete (LWAC) is comparatively lower than that of normal weight concrete (NWC), primarily due to the propensity for fracture exhibited by lightweight aggregates and their characteristics that modify the damage softening mechanism at the crack tip. Few studies have been done on how to precisely predict the LWAC fracture energy. In this work, 111 sets of three-point bending test data were gathered, and the impact of aggregate types and size, concrete density, water-cement (w/c) ratio, and compressive strength on the total average fracture energy (GF) and the initial fracture energy (Gf) was thoroughly evaluated. Five fracture energy prediction methods’ applicability were compared, and a fracture energy prediction expression appropriate for LWAC was presented. Finally, the three-point bending test was used to confirm the prediction. The results show that the fracture energy of LWAC is significantly influenced by changes in aggregate and mortar characteristics. The compressive strength has substantial correlations with the fracture energy of LWAC. After adjusting the aggregate and mortar coefficients, the prediction formula can correctly predict Gf and GF.

Development of low carbon concrete and prospective of geopolymer concrete using lightweight coarse aggregate and cement replacement materials

The use of Ground Granulated Blast-furnace Slag (GGBS) as an alternative cement replacement material in combination with conventional coarse aggregate have been successful in the production of near green concrete. Undoubtedly, GGBS has exhibited good cementitious attributes, however, there are concerns with slow strength development and workability owing to its non-pozzolanic activities as well as some degree of porosity notwithstanding the sustainability potential. Therefore, this study presents a lytag based geopolymer lightweight concrete with high strength development, improved mechanical properties and reduced embodied carbon. To further improve and enhance the potential production of green concrete, complete replacement of conventional coarse aggregate with a recycled lightweight aggregate from industrial waste was carried out. The geopolymer precursors consisted of sodium hydroxide, sodium silicate, GGBS and silica fume to optimize the performance of the concrete at 60–80% cement replacement for a target design mix of 20, 30, 40, and 50 MPa. The performance of lytag based geopolymer concrete was compared with that of non-geopolymer lytag based concrete (control samples). The results show a 42% increase in compressive strength for the geopolymer lightweight concrete and a 22% increase in ultimate compressive strain which is an indication of improved moment of resistance in structural design. The results also show a 46–61% reduction in embodied carbon for the use of non-geopolymer lytag based concrete and 69–77% reduction for lytag based geopolymer concrete. The geopolymer concrete between 7 and 63 days of loading increases by 0.55% in creep strain compared with increases of 2.81% for non-geopolymer lytag based concrete and reduction to 27.96% for the normal weight concrete. Modulus of Elasticity reduces with age of loading for the geopolymer concrete during creep at 0.39% compared to reduction of 1.93% for non-geopolymer lytag based concrete and increase of 12% for the normal weight concrete.

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

Improvements in lightweight concrete T beams CFRP strengthened and anchored with U‐wraps

AbstractThis research provides a study for an experimental program using sand‐perlite‐lightweight reinforced concrete (RC) beams strengthened and anchored with carbon fiber reinforced polymer (CFRP) materials. The main objective of this work is to showcase the efficiency of using U‐wrap anchors to secure the externally applied CFRP sheets on lightweight RC beams. A series of six full‐scale T‐beams with an increasing number of CFRP U‐wraps per shear span was prepared and tested. The use of U‐wrap anchorage enhanced the flexural performance of the sand‐lightweight concrete beams by progressively delaying the premature debonding of CFRP sheets as a direct function of the number of U‐wraps used per shear span. The beam flexural capacity gradually improved from 116 kN without the use of U‐wrap anchors to 182 kN when using six U‐wraps per shear span, which reflects a significant enhancement. Similarly, the ultimate deflection gradually improved from 56 mm for the beam without U‐wrap anchors to 94 mm when applying six U‐wraps per shear span. A design model established earlier, for normal weight concrete, has been successfully qualified to yield accurate findings against the experimental results. Also, the outcome of this study interestingly showed that the ultimate strength results of the anchored beams were close to their counterparts of normal weight concrete conducted on identical beams. This finding shows that U‐wrap anchors performed efficiently despite the lack of coarse aggregate interlock in the concrete mix.

Experimental investigation on flexural behaviour of prefabricated ultra-shallow steel concrete composite slabs

This paper presents the test results of four static full-size four-point bending tests to investigate the flexural behaviour of a recently developed prefabricated steel-concrete composite ultra-shallow flooring system (PUSS®). The flooring system comprises of T-ribbed concrete floors partially-embedded within and connected to side C-channel beams and horizontally-oriented shear connectors. This study investigates the effects of three parameters on the flexural behaviour of PUSS® and the performance of the shear connectors under bending. The parameters under study are the type of concrete, degree of shear connection and depth of the slab. Four 4 m span test specimens are constructed using two types of concrete, two with reinforced normal weight concrete (NWC) and the remaining two with reinforced lightweight aggregates concrete (LWC). Three of the test specimens employ the unique shear connection system composed of horizontally-oriented steel dowels with horizontally-oriented web-welded shear studs (dowels with WWSS) while the last one employs horizontal steel dowels only. The contribution of the above parameters on flexural behaviour and failure mechanisms are examined. The study concludes that replacing NWC with LWC of similar strength does not affect the flexural behaviour of PUSS® in terms of slab capacity, ductility and failure mechanism. However, LWC demonstrates lower initial stiffness and leads to the development of larger cracks as loads increases. Also, reducing the degree of shear connection lowers the moment capacity of the slabs and results in failure of some shear connectors during testing. PUSS® units exhibit ductile behaviour under bending conditions regardless of the degree of shear connection.

Pressure drop and heat transfer properties for normal weight and lightweight pervious concrete

This study examines the performance of pervious concrete when used for heating and cooling through forced air conditions. The influence of aggregate type, water-cement ratio, and paste volume on the air flow characteristics were examined through experimental evaluation of 10 mixes. The thermal properties and sensible heat energy stored in the pervious concrete were evaluated by measuring temperature changes with hot air flow. The results show that at a velocity of 0.35 m/s, the pressure drop falls within the range of 500 Pa/m to 8000 Pa/m. The pressure drop increases with an increase in the volume of paste to volume of aggregate ratio and decreases in water/cement ratio due to changes in the porosity and interconnected void structure of the pervious concrete. A modified pressure drop formulation based on the porosity, volume of paste to aggregate, and water/cement ratio is developed which provides a reasonable prediction for pervious concrete. The energy stored in the concrete can be accurately estimated based on the measured specific heat of the pervious concrete.

SHEAR RESISTANCE OF OIL PALM SHELL REINFORCED CONCRETE BEAMS CAST WITH SHEAR REINFORCEMENT

Research on the use of Oil Palm Shell (OPS) to replace coarse aggregates in concrete to date has been focusing on the material properties of oil palm shell concrete (OPSC). So far, there has been a very limited amount of work conducted to investigate the shear performance of the OPSC beams indicating similar shear strength to that of normal-weight concrete (NWC) beams. This study investigates the shear failure mechanism of OPSC beams cast with shear reinforcement. The test results recorded from 11 OPSC beams and 5 NWC beams, simply supported with two-point loads, are presented. The variables considered include the concrete compressive strength, flexural reinforcement, shear-span, and shear-link spacing. The observed shear failure mechanism of OPSC beams was found to be similar to that of an NWC beam while the shear crack formation and shear resistance of OPSC beams are slightly higher (3% to 14%) and (4.2% to 8.5%), respectively. Comparative studies using the current provisions of EC2 and BS8110 have been performed and found that both codes’ predictions, show good agreement with only a slight overestimation (VTest/VBS of 0.988) on the shear resistance, were consistent with the tests.

Tensile and shear capacity of post-installed chemical adhesive anchors in lightweight concrete

Due to construction efficiency and performance, chemical anchors have been widely applied to long-span or high-rise structures or infrastructures. This study investigates the capacity of post-installed anchors in concrete with lightweight aggregates. Extensive static experiments are conducted to investigate tensile and shear capacities of chemical adhesive anchors in lightweight concrete. Both confined and unconfined tensile conditions are considered. In total, 102 tests are performed with various anchor diameters (12–30 mm), embedment depths (80–300 mm), and types of concrete. The test results show that cone breakout and combined failures dominate the unconfined tensile tests, which have about 40% capacity for the anchors in normal-weight concrete. Chemical adhesive anchor failure models in lightweight concrete are also summarized with respect to the input parameters. Finally, multiple nonlinear regression analyses are further performed, and revised empirical and analytical equations are proposed for lightweight concrete to accommodate different failure modes.

Fracture behavior of concrete made with sintered fly ash lightweight coarse aggregate in comparison to normal weight concrete

Sintered fly ash lightweight aggregate based concrete has been reported to give mechanical and durability properties similar to conventional concrete. But concrete made up of lightweight aggregate possesses lower stiffness and shear strength resulting into a brittle mode of failure due to crack propagating directly inside aggregate which is weak in nature. The study presents findings from the experimental investigation of fracture behavior of concrete made with sintered fly ash lightweight coarse aggregate in comparison to normal weight concrete (NWC) at w/b ratio of 0.5, 0.4 and 0.3. The mixes have been tested for compressive and split tensile strength for both concrete types. On notched beams of size 100x 100 x 500 mm, a three-point bend test has been carried out for both lightweight and normal weight concrete to evaluate fracture parameters. The results of split tensile strength test indicated that the split tensile to compressive strength ratio lies in the range of 5-8% for lightweight concrete and this ratio lies between 5-10% for normal weight concrete. The study indicates comparable fracture behavior for both lightweight and normal weight concrete. The non-linear ascending and descending branches in load vs deflection curve of concrete with sintered fly ash lightweight coarse aggregate can be linked with the non-linearity in tensile type stress-strain behavior and formation of the fracture zone in front of the initial notch. The modulus of elasticity of lightweight concrete is significantly lower than normal concrete. The modulus of elasticity, area under the load deflection curve, tensile strength, fracture behavior etc. needs to be considered appropriately in the non-linear analysis of lightweight concrete.

Effect of Iron ore Tailings on the Water Absorption of Normal Weight Concrete

Most of the important properties of hardened concrete are related to the quantity and the characteristics of the various types of materials in the concrete. In this study, iron ore tailings (IOTs), an inert, industrial waste material, was combined with sand in varying proportion as fine aggregate in concrete. Five concrete samples A, B, C, D and E were produced. Sample A served as control while samples B, C, D and E contains IOTs as partial replacement for sand. Physical properties, Energy dispersive x-ray (EDX) spectroscopy and X-ray fluorescence (ERF) of fine aggregates were determined. Slump and compacting factor of the fresh concrete were also determined. The density, compressive strength, flexural strength, ultrasonic pulse velocity and the microstructure of the hardened concrete were also assessed. The outcome of this study reveals that concrete sample with 40 % iron ore tailings (IOTs), is about 3.7 % denser than the control sample. Concrete sample with 30 % iron ore tailings (IOTs), recorded the highest compressive and flexural strengths. Ultrasonic pulse velocity values and the microstructure of the IOTs concrete samples shows that inclusion of Iron ore tailings in normal weight concrete reduces absorption of water in the concrete.

Experimental determination of creep coefficients for sintered flyash lightweight aggregate based concrete and verification with creep models

The experimental creep coefficient has been determined for two concrete strengths of about 40 MPa and 60 MPa using sintered flyash lightweight aggregate and granite aggregate in creep rig with capacity of 1500kN as per ASTM C-512. The creep results indicate that despite both density and modulus of elasticity being on lower side for sintered flyash lightweight based concrete, the creep coefficient has been lower than that of normal weight concrete with granite aggregate for same strength level. The comparison of existing creep models has been carried out with experimental results for both normal and lightweight concrete considering parameters in models such as relative humidity level, concrete mix ingredients, aggregate properties, oven dry density, elastic modulus of both concrete types etc. considered in study. The creep coefficients have been obtained experimentally at loading age of 28-day and testing period of 365 days and has been compared with existing creep models such as B-3, B-4, ACI-209, EN:1992/FIB. For the similar compressive strength level, creep coefficient of structural grade lightweight concrete is found to be lower in comparison to creep coefficient of normal weight concrete as the internally stored water in porous aggregates keeps capillary pores almost saturated and leaves minimal chance for seepage to occur

Post-fire behavior of lightweight concrete corbels

Corbels are small cantilevers used extensively in precast structures to transfer concentrated loads to columns. Many precast structures are made of lightweight concrete (LWC), and in case they suffer a fire event, investigating the residual strength of their corbels becomes essential. This study aims to examine the performance of LWC corbels exposed to elevated temperatures, present a calculation methodology for estimating their residual capacity, and assess, for the first time, the difference between the behavior of LWC and normal-weight concrete (NWC) corbels. Twelve full-scale reinforced concrete corbels were fabricated with LWC or NWC and different shear span-to-depth ratios and reinforcement details. The specimens were subjected to loading until failure at ambient temperature, either without heat exposure or after exposure to temperatures exceeding 750 °C. Experiencing elevated temperatures reduced the strength of LWC corbels by 44–54%, compared with 33–50% for NWC specimens; though generally similar residual behaviors were observed for LWC and NWC specimens. The strut-and-tie method (STM) provided good estimates of the strength of LWC and NWC specimens if the residual compressive strength of concrete based on the average temperature between the core and the surface of the specimens is used in calculations. The ratio of calculated capacity to measured strength ranged between 0.73 and 1.02 for LWC and between 0.66 and 0.86 for NWC specimens.

Effect of Accelerators on High Early Strength Concrete (HESC) Using High Volume Fly Ash

Applying large quantities of fly ash for the production of High Early Strength Concrete (HESC) is a challenge for researchers in the utilization of quality, inexpensive, and environmentally friendly materials. A high volume of fly ash in concrete, however, reduces the initial compressive strength of the concrete. For this reason, it is necessary to use admixture additives in the concrete mixture to get the expected performance. This research seeks to identify the optimal HESC mix design using fly ash 50% of the total cementitious by adding a superplasticizer and accelerator to obtain a high initial compressive strength. Three variations of HESC, namely HESC-12, HESC-14, and HESC-16, were made using a superplasticizer and accelerator with different doses. Each variation uses 12 liters of superplasticizer and different accelerator volumes: 12 liters, 14 liters, and 16 liters. Specimen testing was carried out on fresh and hard concrete. Fresh concrete was subjected to a slump test, whereas hard concrete was subjected to compressive tests at 18 hours, 24 hours, 3 days, and 28 days of age. The average slump flow values for HESC-12, HESC-14, and HESC-16 (cm) were 78, 79.5, and 80, respectively, demonstrating that all HESC samples are classified as self-compacting concrete (SCC). According to the results of density tests conducted on all specimens ranging from 2461 to 2538 kg/m3, all specimens are included in the category of normal-weight concrete. Within the range of 29.8 to 35.3 MPa for the initial compressive strength of HESC at 24 hours of age, it can be concluded that all HESC specimens fulfill the criteria for high early-strength concrete. The addition of the right type and dosage of chemical admixture is a solution to overcome the weakness of applying fly ash in high-early-strength concrete.

Comparative Study of the Seismic Behaviour of G+20 Storey Building for Unsymmetrical Plan Area Using Light Weight Concrete and Normal Weight Concrete

Abstract: This research examines and compares the performance of structural lightweight concrete (SLWC) made with scoria and normal weight concrete (NWC), and normal and light weight concrete (NAL) in multi-storey buildings. A G+20 multi-storey unsymmetrical plan building is analysed using the response spectrum method with SLWC and NWC. Bending moment, shear force, storey shear, axial force, storey drift, and storey displacement are considered. The results show that SLWC can be used to reduce the weight of buildings without sacrificing strength or performance. This can lead to significant cost savings on construction and materials

Properties of Fine Graded Perlite-Based Lightweight Cement Mortars Subjected to Elevated Temperatures

The present research compared the behaviours of lightweight mortars based on ordinary Portland cement (OPC), calcium sulphoaluminate cement (CSAC), and calcium aluminate cement (CAC) containing expanded perlite and subjected to elevated temperatures. The perlite substituted natural sand in amounts of 25, 50, 75, and 100% by volume. The mortars were subjected to heating at up to 300 °C, 650 °C, and 1000 °C at a rate of 20 °C/min. The consistency and density of fresh mortars, compressive strength and density of hardened mortars after heating and cooling, and absorbability were assessed. Such a holistic testing approach is the main novelty of this research, which is related to the aforementioned mixtures and elevated temperatures. The main contribution of this article is a comparison of various cement types coupled with variations in the level of sand replacement with expanded perlite. In previous studies, comparisons were made in pairs of OPC-CSAC and OPC-CAC for normal-weight concrete. There is a gap in our knowledge of triple comparisons and lightweight cement composites which is filled by the current study. The use of OPC at up to 650 °C is recommended because it is the most common solution, its performance is similar to that of CAC, and it is cheaper than other solutions. Above 650 °C and up to 1000 °C, CAC is the only solution because it performs better than other cements. CSAC is not suitable for use at elevated temperatures because of its poor strength performance, even if it is the best solution from an environmental point of view. Sand replacement with perlite does not increase the strength performance under elevated temperatures, but its efficiency is different for various types of cement.

Comparative Study of Glass Fiber Reinforcement in Lightweight and Normal Weight Concrete

Comparative Study of Glass Fiber Reinforcement in Lightweight and Normal Weight Concrete

Pumping lightweight aggregate concrete into high-rise buildings

Lightweight aggregate concrete (LWAC), characterized with low density and high crushing strength to apparent density ratio, is a potential construction material for modern concrete structures. However, experiences in pumping LWAC to high-rise buildings are insufficient and the pumping pressure of fresh concrete may differ from normal weight concrete (NWC). Herein, three groups of shale lightweight aggregate (SLWA) were prepared to evaluate the workability of LWAC before and after pumping up to 102-m construction site. Water content and pressure loss are analyzed to understand the mechanism in slump variation of LWAC. A pumping pressure model is proposed based on friction assumption for horizontal and vertical pumping. The relationship between water content and ambient pressure is simulated. Pressure drop in pumping LWAC is found more than 4 times that in NWC at the same slump level. The main reason for large slump loss and pumping difficulty for LWAC lies in the water transportation process from mixture into porous aggregates.