Interface shear strength of composite concrete-to-concrete bond

Interface shear strength between two concrete layers cast at different times plays an important role to develop composite action of the floor slabs. Most previous studies when quantifying interface shear strength for interface concrete with projecting steel did not take concrete cohesion into consideration. In contrast, interface concrete without projecting steel depended solely on concrete cohesion in quantifying the interface shear strength. Although there are studies conducted on the action of interface shear strength under variable normal stresses, the findings only considered smooth or left “as-cast” surface. Furthermore, Finite Element Modeling (FEM) of the interface shear behavior for concrete-to-concrete bond is also limited in research. In this study, a total of 72 “push-off” tests were carried out to study the interface shear strength of composite slab with six different surface textures. This included smooth or left “as-cast”, roughened by wire-brushing in the longitudinal and transverse direction, groove, indented and projecting steel crossing the interface. Loading was then applied horizontally on the concrete topping until failure was observed under various normal stresses; ?n = 0 N/mm2, 0.5 N/mm2, 1.0 N/mm2 and 1.5 N/mm2. The relationship between surface texture, interface shear strength and normal stress was then proposed in this study. The roughness profile of the concrete base was measured using a portable stylus roughness instrument

Interface shear strength of concrete-to concrete bond with and without projecting steel reinforcement

Composite concrete consists of two elements cast at different times which are the concrete base and concrete topping. To achieve composite action, interface shear strength must be sufficient to resist the sliding motion between the two concrete surfaces in contact. The interface shear strength is mainly depended on concrete cohesion, friction and dowel action. A total of 36 “push-off” tests were performed to study the interface shear strength and to assess the influence of surface texture and steel reinforcement crossing the interface. Three different concrete base surfaces are prepared which include smooth or “left as-cast”, roughened by wire-brushing in the transverse direction and steel reinforcement projecting from the concrete base. Eurocode 2 provides design equations for determining the interface shear strength with different surface textures and also the one where projecting steel reinforcement crosses the interface. The experimental results show that the transverse roughened surface produced the highest interface shear strength of 1.89 N/mm2 (sn = 0 N/mm2), 4.69 N/mm2 (sn = 0.5 N/mm2), 5.97 N/mm2 (sn = 1.0 N/mm2) and 6.42 N/mm2 (sn = 1.5 N/mm2) compared with the other surface textures. This proves that the increase in the degree of roughness contributes to higher concrete cohesion and friction coefficient. However, for the surface with projecting steel reinforcement, the failure is not sudden as experienced by the surface without one. This is due to the contribution of the clamping stress from the dowel action of the steel reinforcements. Meanwhile, for specimens without any projecting steel reinforcements, the interface shear strength depended solely on friction and concrete cohesion of the surface textures. The interface shear strength of surface with and without the projecting steel reinforcement can be predicted using the Mohr-Coulomb failure envelope. This paper also proposed design expressions for concrete-to-concrete bond on surfaces provided with and without projecting steel reinforcement that can be adopted in Eurocode 2

Finite element modelling of interface shear strength at concrete-to-concrete bond

Interface shear strength between concrete layers cast at different times plays an important role to provide monolithic behavior of composite concrete. In this paper, a computational modeling approach is used to study the concrete-to-concrete bond behavior between two concrete layers cast at different times; concrete base and concrete topping. The compressive strength of the concrete base is 40 N/mm2, while the concrete topping is 25 N/mm2. Finite Element Analysis (FEA) package ABAQUS 6.12 is used to model the bond interaction of concrete-to-concrete layers, which is then verified with the experimental test. Four specimens with different types of surface textures are - -brushing in transverse direction and projecting steel reinforcement crossing the interface. Failure of the bonded interfaces is modeled with cohesive zone model (CZM) approach with zero thickness interface element where the governing parameters are - meanwhile, the projecting steel surface is modeled with Modified Drucker-Prager/Cap-Plasticity Model (CPM) approach with 1 mm thickness of interface element. The parameters used in the analysis include interface shear strength, fracture energy and elastic shear stiffness for CZM approach. The CPM parameters for modeling projecting steel surface are cohesion, interface friction angle, cap eccentricity parameter, initial cap yield surface position, flow stress ratio, yield stress at interface. The study shows that the difference between the modeled and experimental results is relatively small and therefore shows the capability of the finite element analysis to carry out interface analysis

Finite element modeling of the interfacial behavior at surface roughness concrete without the projecting steel

The development of composite action between precast concrete slab and concrete toppings is important to provide a monolithic behavior of composite concrete. The current Eurocode 2 provides design expression for interface shear strength of both concrete base and concrete topping. In this paper, the finite element modeling is presented and calibrated with experimental results. The interface shear strength between precast concrete slab and cast-in place concrete topping slabs was evaluated through a set of 9 push-off experiments. Finite Element Modeling package ABAQUS 6.12 was used to model the interface bond of concrete-to-concrete layers. The push-off test specimens featured segments of precast concrete slabs sized 300 mm × 300 mm × 100 mm with a variety of surface textures including trowel finished, indented and wire-brush roughened. A cast-in place concrete was poured on top of the concrete base to form a 300 mm × 300 mm × 75 m concrete topping. Failure of the bonded interfaces was modeled with cohesive zone model (CZM) approach with zero thickess interface element. The parameters used in the analysis include interface shear strength, fracture energy and elastic shear stiffness. The study shows that the difference between the model and experimental results is relatively small and therefore shows the capability of the finite element modeling to carry out interface analysis

Synthesis and characterization of CaO-TiO2 for transesterification of vegetable palm oil

This study explores the potential of titanium oxide impregnated on calcium oxide (CaO-TiO2) as catalyst in transesterification of vegetable palm oil (VPO) to produce biodiesel. The biodiesel yield increased with catalyst calcination temperature and reaction time, and the usage of CaO-TiO2 led to higher yield of biodiesel production when compared to reaction catalyzed by CaO. Biodiesel yield of 93.33% was recorded when CaO-TiO2 was used at optimized reaction conditions. Catalyst characterizations showed that addition of TiO2 to CaO improved the catalytic property by increasing the surface area and strength of basic sites, hence increased the catalytic performance of CaO-TiO2. This study demonstrates the potential of CaO-TiO2 to convert VPO into biodiesel, and the potential of the catalyst in the conversion of waste cooking oil into renewable fuel

One-way transnational magnetic mass damper model for structural response control against dynamic loadings

Structural responses should be reduced to minimize the consequent structural damage caused by dynamic excitation. The one-way translational magnetic mass damper model is developed as a new type of damper for the purpose of structural response control. The damper utilizes the concept of repulsive force between magnets with same poles to create a magnetic force to stabilize or bring the structure back to its original position. The dynamic performance of the structure was tested using a harmonic shaking table. In this study, the three parameters used are excitation speeds: 2.5V (low), 6.0V (medium) and 8.5V (high); strength of magnets: weak (N35), medium (N45) and strong (N52); and the mass in the damper: 40 g, 101 g and 162 g. The correlations of the parameters towards the structural displacement are verified in the testing. The displacement is highly reduced up to 100% at the first level and 85.2% at the fifth level. The most optimum structural response control was attained when a strong magnetic strength and mass of 162 g are used. When tested with three excitation speeds; 2.5V, 6.0V and 8.5V, the damper with this setting provides the optimum damping effect towards the structure in terms of displacement

Improving sustainability of road construction by partial replacement of natural aggregates in subbase layer with crushed brick and reclaimed asphalt pavement

Reducing dependent on naturally sourced materials is among the priority in improving the sustainability of road construction. The subbase layer which provides strength and stability across the road profile, comprised mainly of natural aggregates. This study aims to explore the feasibility of partial replacement of natural aggregates in subbase layer with 20% Crushed Brick (CB) and 20 to 50% Reclaimed Asphalt Pavement (RAP). California Bearing Ratio (CBR) test and Constant Head Permeability tests were carried out to determine the effect of this partial replacement on the geotechnical properties of the subbase layer. The results obtained denotes that the combination of 20% CB and 50% RAP is the optimum partial replacement of natural aggregates in subbase layer with CB and RAP. The use of CB further complements RAP in improving the stiffness and compressibility of the subbase layer while contributing significantly toward sustainability in road construction

Microstructural Characterization of Fibric Peat Stabilized with Portland Cement and Silica Fume

Peat is a renowned problematic soil and needs stabilization to enhance its engineering properties. Silica fume (SF) and Ordinary Portland Cement (OPC) were extensively adopted to increase the mechanical properties of peat; however, their microstructural analysis is lacking. Investigated herein is the microstructural evolution caused by the OPC and SF implementation in peat soil stabilization. Initially, the compositional analysis (elements and oxides) of peat and binders was carried out via energy-dispersive X-ray (EDX) and X-ray fluorescence (XRF). Subsequently, the microstructural changes that occurred in the stabilized peat were examined through a series of microstructural analyses. The analysis includes scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and thermogravimetric analysis (TGA) for morphological, mineralogical, functional group analysis, and bond thermal analysis, respectively. The SEM micrographs evidence the transformation of loosely packed with large micropores of untreated peat into a compact dense peat matrix. This transformation is due to the formation of newly developed minerals, i.e., calcium hydrates (CH), calcium silicate hydrates (C-S-H), calcium aluminate hydrate (CAH), ettringite (Aft) caused by the pozzolanic reaction of binders as recorded by the XRD. Similarly, different molecular functional groups were found in the FTIR analysis with the incorporation of SF and OPC. Finally, the percentage of mass loss was assessed through TGA analysis revealing the decomposition of stabilized in the second and third stages

Palm Oil Fuel Ash (POFA) and Eggshell Powder (ESP) as Partial Replacement for Cement in Concrete

This study is an attempt to partially replace Ordinary Portland cement (OPC) in concrete with palm oil fuel ash (POFA) and eggshell powder (ESP). The mix proportions of POFA and ESP were varied at 10% of cement replacement and compared with OPC concrete as control specimen. The fineness of POFA is characterized by passing through 300 μm sieve and ESP by passing through 75 μm sieve. Compressive strength testing was conducted on concrete specimens to determine the optimum mix proportion of POFA and ESP. Generally the compressive strength of OPC concrete is higher compared to POFA-ESP concrete. Based on the results of POFA-ESP concrete overall, it shows that the optimum mix proportion of concrete is 6%POFA:4% ESP achieved compressive strength of 38.60 N/mm2 at 28 days. The compressive strength of OPC concrete for the same period was 42.37 N/mm2. Higher water demand in concrete is needed due to low fineness of POFA that contributing to low compressive strength of POFA-ESP concrete. However, the compressive strength and workability of the POFA-ESP concrete were within the ranges typically encountered in regular concrete mixtures indicating the viability of this replacement procedure for structural and non-structural applications