The utilization of marine waste and resources to produce eco-friendly building materials is essential for the sustainable development of the construction industry on islands and coastal areas. The ...sea sand and coral sand sourced from coral waste are the most promising. Therefore, the objective of this work is to investigate the feasibility of coral/sea sand as fine aggregate to prepare an environment-friendly marine mortar. The effects of various volume fractions of coral sand intended to replace sea sand on the flowability, physical performances, carbonation resistance, and microstructure of the prepared marine mortars were evaluated. The experimental results showed that as the sea sand replacement by coral sand was increased, the flowability and dry bulk density decreased, while the water absorption increased. Encouragingly, usage of a combination of coral and sea sands enhanced the flexural strength of marine mortars. A mixture containing 80 vol% of coral sand showed the best effect. The carbonation depth of marine mortar was found to noticeably increase with increasing replacement ratios of sea sand by coral sand, closely relating to the increase in the volume of capillary and large pores. In particular, the combined utilization of coral sand and sea sand resulted in a compacted interfacial transition zone (ITZ) between fine aggregates and the matrix.
•Physical properties and carbonation resistance of marine mortar were evaluated.•The addition of coral sand can improve the flexural strength of marine mortar.•Incorporating coral sand markedly increase the carbonation depth of marine mortar.•Combined use of coral and sea sands in marine mortar can promote compaction of ITZ.
In this paper, a new type of green reactive powder concrete (GRPC) with compressive strength of 200
MPa (C200 GRPC) is prepared by utilizing composite mineral admixtures, natural fine aggregates, ...short and fine steel fibers. The quasi-static mechanical properties (mechanical strength, fracture energy and fiber–matrix interfacial bonding strength) of GRPC specimens, cured in three different types of regimes (standard curing, steam curing and autoclave curing), are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the cementitious materials consisting of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume, 4% volume fraction of steel fiber are higher than the others. The corresponding compressive strength, flexural strength, fracture energy and fiber–matrix interfacial bonding strength are more than 200
MPa, 60
MPa, 30,000
J/m
2 and 14
MPa, respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the Split Hopkinson Pressure Bar (SHPB) according to the spalling phenomena. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of C200 GRPC. With an increase of strain rate, the peak stress rapidly increases in the dynamic tensile stress–time curves. The C200 GRPC exhibits an obvious strain rate stiffening effect in the case of high strain rate. Finally, the mechanism of excellent static and dynamic properties gains of C200 GRPC is also discussed.
This study investigates the flexural behavior of UHPC materials containing steel fibers of varying lengths. Mesomechanical analysis is performed according to the analytical pullout model, using ...actual measured fiber distributions. The flexural behavior of UHPC after cracking is simulated by superposing the fiber bridging and matrix softening curves. Subsequently, the evolution of stress–strain along the axial crack of UHPC is evaluated under different loading conditions. The obtained results indicate that longer steel fibers can efficiently improve the flexural behavior of UHPC. Moreover, the actual fiber orientation and pullout length distributions can be well fitted by two-parameter probability distribution (PDF) and Gaussian functions, respectively. Based on the micromechanical analysis, the fiber bridging behavior is overestimated under the assumption of 2D random fiber distribution, and it is underestimated under the assumption of 3D random fiber distribution. Interestingly, the length of the shear lag zone is independent of the fiber length, which is about 20.16 mm. The obtained results demonstrate that the compressive stress and strain at the top of the tested specimen gradually transform into tensile stress and strain at the opposite side. Interestingly, the stress of the specimens with fiber length of 20 mm are slightly higher than the specimens with fiber lengths of 6 and 13 mm, and the strain just lower than the specimens with fiber lengths of 6 and 13 mm in all crack propagation stages, respectively. This indicates that, in addition to the number of steel fibers, the stress/strain dispersion depends on fiber length.
This study investigated the fatigue crack propagation behavior of ultra-high-performance concrete (UHPC) incorporated with different steel fiber lengths of 6, 13, and 20 mm under flexural cyclic ...loading, based on the Paris law and nonlinear fracture mechanics. In addition, multiple crack covering areas and fatigue J-integral amplitudes were employed to quantitatively evaluate the fatigue crack propagation rate and predicate the fatigue life of the UHPC during the steady development stage. The results indicated that the maximum crack opening displacement (COD) values were 0.312, 0.673, and 1.265 mm and the minimum crack growth rates were -3.05, -4.48 and -4.62 for SF6, SF13, and SF20, respectively. The critical crack length was approximately 65 mm for UHPC specimens containing different fiber length at a given fiber volume fraction (2.0%), indicating that the critical crack length was simply related to the fiber length. Interestingly, when the fatigue crack area of all the tested series reached approximately 35 mm2, fracture failure occurred. There were very small predictions between the actual tested and predicated fatigue lives, all less than 7.21%. Hence, it was reasonable to predict the fatigue life of the UHPC based on the J-integral according to the DIC technique.
Experimental research on water vapor adsorption performance of concrete with different class Ⅱ fly ash contents is carried out in this paper. Time-varying response curves of water vapor adsorption of ...fly ash concrete in five different humidity environments were obtained. According to the empirical formula of the thermodynamic parameters of water vapor adsorption of cement-based materials, the thermodynamic parameters of the water vapor adsorption process of fly ash concrete materials are calculated. The calculation method of the thermal kinetic parameters of water vapor adsorption for fly ash concrete materials is proposed; Influence of different fly ash contents with 10%, 20% and 30% mass percentage of cement and water-cement ratio on the water vapor adsorption characteristics of concrete materials is analyzed; The error between the second-layer adsorption energy and the condensation enthalpy of water vapor is calculated, and the rationality of the approximate calculation is analyzed. It is noted that (1) Water vapor adsorption characteristics of concrete materials are related to the water-cement ratio. With the water-cement ratio decreases, the adsorption capacity of concrete material increases. (2) Reasonable formula for calculating the number of saturated adsorption layers n of water vapor suitable for concrete materials is recommended. (3) Taking the condensation enthalpy of water vapor as the adsorption enthalpy of the second layer and subsequent layers reasonable to determine the dynamic parameters of the water vapor adsorption process of concrete.
Concrete has complex pore structure characteristics, and a variety of pore structure testing techniques, including nitrogen absorption and desorption method, mercury intrusion porosimetry, gravimetry ...method, scanning electron microscopy, industrial computerized tomography, etc., were used to characterize the pore structure characteristics of fly ash concrete. Porosity, pore size distribution, specific surface area, and characteristic pore size were studied by MIP and NAD. The tortuosity was calculated by the corrugated pore structure model of the MIP method. The interfacial transition zone of the microstructure is studied by scanning electron microscopy and industrial computerized tomography. The results show that the fly ash content in the range of 10∼30 % could increase micro- and meso-pores in concrete material which is called the refining effect. In the range of 10∼30 % of fly ash content, the three characteristic apertures decreased with the increase of fly ash content. Effect of sample sizes on porosity was gained by NAD and GM methods. The tortuosity of concrete pore structure is between 4 and 9 and fly ash content has no obvious influence on this pore character. SEM imaging of the interfacial transition zone showed obvious defects, and the results of SEM and industrial computerized tomography showed that the width of the interfacial transition zone ranges from 3μm to 168.88μm.
In this paper, water vapor desorption tests are carried out on water-saturated concrete materials with different water-binder ratios and fly ash content. The desorption parameters are analyzed using ...the adsorption curve analysis method, which enables the acquisition of desorption characteristics for concrete materials. By utilizing the desorption isothermal curve, the desorption rate is calculated and further analysis is conducted on the influence of water-binder ratio and fly ash content on this rate. The results indicate that the desorption and activation energy for water vapor desorption in concrete materials is higher than the adsorption energy at the first layer, suggesting that removing water vapor from inner pore walls is more challenging than its adsorption. The amount of water vapor released from concrete materials follows a power function over time, as does the rate of desorption. Under conditions of relatively low ambient humidity, an increase in the water-binder ratio leads to a decrease in the rate of desorption. Conversely, under relatively high ambient humidity, an increase in the water-binder ratio results in an increased rate of desorption.
Impact Resistance of Reactive Powder Concrete Jiao, Chujie; Sun, Wei
Journal of Wuhan University of Technology. Materials science edition,
08/2015, Letnik:
30, Številka:
4
Journal Article
Recenzirano
The impact behaviour of three types of reactive powder concretes （RPC） was studied using the split Hopkinson press bar （SHPB） testing method. These RPC were prepared with steel fiber volume fraction ...of 0%, 3%, and 4%, respectively. The stress-strain relationship, strain rate sensitivity threshold value, dynamic strength increase factor, modulus of elasticity and failure pattern of these RPC specimens subjected to impact load were investigated. From the tests, the strain rate sensitivity threshold value of 50 s-1 was obtained. The experimental results showed that when the strain rate increased from the threshold value to 95 s-1, the maximum stress of RPC increased by about 20% and the modulus of elasticity of RPC increased by about 30%. The failure pattern of RPC specimens with steel fiber reinforcement was very different from that of the RPC matrix specimen when subjected to impact loading. Under similar impact loading rate, cracks developed in the steel fiber reinforced RPC specimens, whilst the RPC matrix specimens were broken into small pieces.
The interfacial transition zone (ITZ) and fly ash content affect the transmission performance of concrete by altering its pore structure, while varying water content also has distinct effects on ...transport characteristics. Therefore, this paper investigates the effects of ITZ, fly ash content, and saturation degree on the gas transport performance of concrete materials through gas penetration tests, mercury injection tests, scanning electron microscopy (SEM), and backscattered electron (BSE) imaging. The influences of these factors on the intrinsic permeability of concrete materials are quantitatively analyzed through methods such as parallel test comparative analysis, regression analysis, function fitting, and fixed parameter analysis. The results indicate that the incorporation of fly ash can refine the pore structure of concrete, but it also leads to an increase in intrinsic permeability. The relationship between saturation degree of concrete and intrinsic permeability conforms to an exponential function. Under the same volume fraction, the intrinsic permeability of ITZ is hundreds of thousands of times higher than that of mortar matrix.
•The full debonding strain between steel fibers and the UHPC matrix is about 0.32%.•The maximum strain for generating cracks is about 3.25%.•The crack initiation strain rate varies linearly with ...time.•The relationship between crack length and temporal crack evolution is described by an exponential function.
This study investigates the crack propagation behavior of UHPC blended with straight steel fibers of different lengths (6, 13, and 20 mm), at varying replacement ratios (0.5%, 1.0%, and 1.5%) and a constant total fiber volume fraction (Vf = 2.0%), under flexural loading. The results indicate that blending with 0.5% medium length fibers and 1.5% long fibers yields the best flexural behavior compared to other investigated specimens. Using digital image correlation (DIC) technique, the evolution of surface deformation and strain field was analyzed. Based on the recorded images and corresponding analyses, the full debonding strain between the fibers and the matrix was determined to be about 0.32%. Moreover, the maximum strain for generating cracks was approximately 3.25%, irrespective of the fiber length. When longer fibers were replaced with shorter fibers at 0.5% or 1.0% replacement ratios, Crack opening displacement (COD) variations along the beam presented a linear shape. However, at higher replacement ratios (1.5% and 2.0%), the profile showed an abrupt change, and COD variations were non-constant. The samples comprising hybrid fibers presented a faster decline in the crack initiation strain rate at higher replacement ratios of the longer fibers. In the initial stage of cracking, the crack propagated rapidly; however, the crack propagation speed dropped dramatically during crack evolution before it stabilizes.
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