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The estimation of the concrete unit cost in construction engineering plays a vital role in controlling construction costs and ensuring timely project completion. To achieve this, a fast estimation algorithm for concrete unit costs is proposed. To ensure accurate estimation and reduce the computational burden on the convolutional neural network (CNN) for rapid estimation, the factors influencing concrete costs are identified and arranged using the interpretive structural modeling (ISM) method. The factors affecting the concrete unit cost of high-rise construction are selected as the input data sequence for the CNN model. The feature map of the input data is extracted through the convolution layer. After applying the pooling operation to the feature map, the processed data is passed into the fully connected layer through the final pooling layer, where the final calculation is performed to obtain the estimated concrete unit cost. Experimental results indicate that to ensure fast convergence and minimize estimation errors in CNN estimation, optimal network parameters are determined through multiple experiments. The best configuration includes a $3\times 3$ convolution kernel and 11 convolutional cores. This algorithm, which uses the ISM method to select influential factors, achieves high accuracy in estimating the concrete unit cost. In actual engineering applications, the error between the estimated and actual results is minimal, with a maximum difference of only 1 yuan.

This study conducted an evaluation of elemental composition of concrete in an old nuclear reactor facility using the particle-induced X-ray emission (PIXE) technique. Given that the physical volume of the concrete is huge, easy, and quick analysis of many samples via the PIXE method can expedite the decommissioning work. The result of this study confirmed that it is possible to use the PIXE method for detecting light and medium-heavy elements (from Na to Fe) in concrete without the complicated chemical treatment. Some of these elements contain parent nuclides of Na-24, Al-28, and Fe-55, which are dominant components with residual radioactivity for a period of up to 10 years after facility shutdown.

In this research, we have carried out the fundamental research on development of high strength concrete using the powder combining three industrial by-products as substitute of cement. The by-products used were fly ash of type II, ground granulated blast-furnace slag and gypsum. As a result,-it was possible to make a high strength paste, using vibrating compaction, with a water-powder ratio of 25%, The paste had compressive strength greater than 60 N/mm² after curing for 91 days. Further we found it was possible to make high strength concrete of varying sand-aggregate ratios which all had a compressive strength of about 30 N/mm² after curing for 28 days and 40 N/mm² after curing for 91 days. Finally we obtained the optimum mixture proportion of concrete is unit water content = 170 kg/m³, water-powder ratio = 25%, and sand-aggregate ratio = 40%, For each of these results no cement was used.

The Vertical continuous mixer has number of mixing units connected in series. When using this mixer in the vertical way, mixing work can be done under gravity force only with the new modified mechanism of inter-particle collision and impact. The mixing process inside the vertical continuous mixer is totally different from that of existing mixers. The aims of this paper are to clarify the mechanism of mixing process of the vertical continuous mixer with gravity and to obtain the useful information on the design of a high-performance vertical continuous mixer with help of the visualization technique. The results of this study indicate that it is very important that the accumulation time of materials through mixing units is long and that the fluctuation of velocity of materials falling and the fluctuation of angle of materials falling are large as long as the blockade of materials does not happen in order to increase the mixing efficiency of vertical continuous mixer.

In this paper, three types of projectiles were designed, which are based on the physical mechanism of high-speed penetrating into concrete targets. The three types of projectiles are ogive nose followed by cylinder, cone and grooved cone shank respectively, which are made of 30CrMnSiNi2A with the yield strength 1570MPa. The unconfined compressive strength of concrete target for test is 50MPa. Seven experiments for striking velocities between 800 and 1100m/s were conducted. The experiments showed that the projectiles of cone and grooved cone shank have better penetration performances and the penetration channels were very straight. Compared with the cylinder shank projectiles, the cone and grooved cone shank projectiles are more effective under the condition of high velocity penetrating into complex geological materials as concrete or rock.

The RHT concrete strength model and failure model are employed for the numerical simulations of composite projectile penetrating concrete targets. The simulations show that RHT parameters, specially the failure parameters, greatly influence the penetration depth, exit velocity. The failure mode of concrete should be paid great attentions in numerical analysis. If the crushing failure is the primary mechanism, RHT model seems effective. For the cracking process of concrete, the model should be tensile failure description. Reasonable material parameters are important in penetration simulations. Comparison between numerical analysis and experimental date is made for discussion about the parameter effects.

In this paper, a multi-scale modeling approach is used to study the effect of adding graphene sheets to concrete matrix on the thermal conductivity of the concrete. By computing the thermal conductivity of the graphene along the armchair and zigzag directions using molecular dynamics (MO) simulations, it is shown that the graphene sheets have orthotropic thermal behavior. Therefore, at the upper scale, in which the finite element (FE) method is used to obtain the thermal conductivity of the concrete/graphene nanocomposites, the graphene sheets are considered as orthotropic continuous sheets. It is shown that the improvement of the concrete thermal conductivity by adding the graphene sheets is directly related to the graphene sheet volume percentage and cross-sectional dimensions.

In this paper, a rectangular split ring resonator-type metamaterial (MTM) sensor application is demonstrated in order to examine concrete materials. First, different types of concrete materials including carbon steel fiber with the purity ratio of 0.5%, 1% and 1.5% were prepared by using cement and water and their electrical properties were determined via Nicolson–Ross–Weir tehcnique. After that, compatible MTM-based sensor structure was designed and proposed. In order to find out the effect of the humidity on the concrete material, all samples were kept in the water pool for 28 days, the samples were then taken out and the temperature effect on the concrete materials was observed by increasing the heat up to 30${}^{\circ }$ and 70${}^{\circ }$ in the oven. The simulated resonance frequency shifts were observed at 910 MHz for concrete material sensor, 120 MHz for humidity sensor validation and 400 MHz for temperature sensor applications. By having large bandwidth in different fiber contents and validating the physical sensor applications as temperature and humidity, it was shown that the proposed study has novelty in the area of MTM-based sensor applications when it is compared with current state-of-the-art.

Electromagnetic wave (EMW) pollution adversely affects information, facilities safety, and human health, leading to the development of EMW absorbing materials, especially absorbing concrete. Here, the influence of arrangement ways of concrete iron on microwave reflectivity was analyzed, and a split ring resonator (SRR) was designed and introduced to steel-reinforced concrete to improve the EMW absorbing performance of the concrete. The simulation results show that by tuning the diameter and arrangement ways of concrete iron and introducing SRR structure, an EMW absorption concrete which can display 0.3% reflection loss ($>90$% absorption) at 2.34GHz was designed and realized. The reflectivity of concrete iron and EMW absorption capacity of concrete were investigated by a vector network analyzer, and the experimental results almost agree with the simulation results. The reflection and absorption of EMW are caused by magnetic resonance and conductive loss, magnetic loss, respectively.

In this paper, the effect of water-cement ratio and chloride ions on the concrete meso-structure was studied. Three kinds of concrete cubes with different water-cement ratios were immersed in fresh water and salt water, respectively. Then, the Electrochemical Impedance Spectroscopy (EIS) analysis of various test cubes were carried out by using electrochemical workstation. The results show that the salt water can improve electric double layer capacitance in the test cubes with the same water-cement ratio, but it can reduce some other parameters such as resistance of pore solution, resistance to transfer the hydrated electron, coefficient of diffusion impedance of concreter, which shows that the chloride ions diffused into the concrete in salt water and increase the ionic concentration in pore solution and C-S-H gel. However, the phase angle index is constant whether in fresh water or salt water, which shows chloride ions cannot affect the concrete meso-structure even though they can improve the ion concentration of pore structure. For the concrete test cubes which has different water-cement ratio in salt water, with the reduction of water-cement ratio, the electric double-layer capacitance of concrete remains unchanged, which indicates when the water-cement ratio becomes smaller, the porosity becomes lower, and the internal structure of concrete becomes denser.

An approximate explicit method from literature to estimate the corrosion initiation time of steel reinforcement in concrete is developed to incorporate random variables which affect the diffusion rate. The method accounts for uncertainties of input parameters and predicate expected time of first corrosion for the chosen risk of corrosion and its variance. Method is also utilized to rank the sensitive parameters to initiate steel reinforcement corrosion. Corrosion is initiated when the chloride concentration on steel reinforcement exceeds a threshold value. Corrosion initiation time is useful for owner, designer, or to an organization to take decision in time of priority of repairs, repair strategy, corrosion protection in order to optimize maintenance planning and budgeting. Planned maintenance at the optimum time is the safest and most cost effective approach.

Reinforced concrete is one of the widely used construction materials for bridges, buildings, platforms and tunnels. Though reinforced concrete is capable of withstanding a large range of severe environments including marine, industrial and alpine conditions, there are still a large number of failures in concrete structures for many reasons. Either carbonation or chloride attack is the main culprit which is due to depassivation of reinforced steel and subsequently leads to rapid steel corrosion. Among many corrosion prevention measures, application of corrosion inhibitors play a vital role in metal protection. Numerous range of corrosion inhibitors were reported for concrete protection that were also used commercially in industries. This review summarizes the application of natural products as corrosion inhibitors for concrete protection and also scrutinizes various factors influencing its applicability.

This paper evaluates performance of three representative single-person walking excitation models which can be used to check vibration levels of high-frequency building floors accommodating highly sensitive equipment. The three models calculate vibration responses by harmonic, transient and spectral analyses, respectively.

The evaluation was based on a combined experimental and analytical work comprising modal testing of a prototype floor, repeated measurements of walking-induced vibrations, finite element modelling and model updating to match the measured modal properties. The updated and verified model was then used for the application of the three walking models results of which were then compared with their experimental counterparts.

It was found that all three models were on the "safe" side and overestimated responses measured in all response tests. However, the harmonic model which assumes high-frequency floor resonance caused by the 7th or 8th harmonic of the walking resulted in over-conservative response estimates order of magnitude higher than the maximum measured values in all response tests. Nevertheless, the model which describes walking across a high-frequency floor as pulses representing footfalls consistently overestimated responses by just about 20% and is, therefore, recommended for vibration serviceability checks of this type of floors.

Results from finite element modeling (FEM) of large-scale steel-concrete composite beams strengthened in flexure with prestressed carbon fiber-reinforced polymer (CFRP) plate were validated with experimental results and presented in this paper. The effect of varying the level of prestressing as percentage of the ultimate tensile strength of the CFRP plate was investigated. Comparison was carried out in terms of overall load-deflection behavior, strain profile along the length of the CFRP plate, and strain distribution across the depth of the beam at mid-span section. Very good agreement was observed between the finite element (FE) and the experimental results. The validated FE models were used to perform a comprehensive parametric study to investigate the changes in the behavior through wider range of prestressing levels and then, determine the optimum prestressing level that maintain the unstrengthened beams' original ductility (or energy absorption). An iterative analytical model was also developed, validated with both the FE model and the experimental results, and showed good agreement. A parametric study was carried out to investigate the effect of changing the yield strength of the steel and the concrete compressive strength on the moment of resistance of the section and the strain in the CFRP plate at ultimate.

This paper presents an experimental investigation of the performances of concrete-filled glass fiber-reinforced polymer (GFRP) and GFRP externally wound steel circular tubes, subjected to freeze-thaw cycles ranging from -18°C to 18°C. The variation in hoop strains of the tubes during the freeze-thaw cycles was monitored by embedded fiber Bragg Grating (FBG) strain sensors in GFRP layers or between GFRP and steel tube. The residual hoop strain after each freeze-thaw cycle indicates the possible degradation of GFRP materials, such as cracks, debonding of GFRP-concrete or GFRP-steel due to mismatch of the coefficient of thermal expansion, as well as water immersion. A synergistic effect of FRP and steel tubes on the confinement of inside concrete was revealed, resulting in well-improved ductility. After 56 freeze-thaw cycles, remarkable degradation were found in the axial strength, modulus, and strain for concrete-filled GFRP tubes. However, the GFRP-steel tube system showed a negligible reduction in the ultimate axial strain by the freeze-thaw cycles with less degradation in the axial strength and modulus.

In order to study isolation measures for plate-shell integrated concrete liquid storage structure (PSICLSS), shaking table tests were carried out to investigate the seismic responses of PSICLSS. The isolation performance of rubber isolation and sliding isolation bearings for PSICLSS was studied and shape memory alloy (SMA) was used to reduce the residual displacement of sliding isolation PSICLSS. The results show that the sliding isolation bearing can effectively reduce the seismic response of PSICLSS; however, there is a large residual displacement in the isolation layer. On the other hand, SMA-sliding isolation can provide a reliable recentering capability for isolating PSICLSS and does not cause amplification of structural response.

This study reviews our recent efforts in the development and application of crack propagation modeling approaches based on the scaled boundary finite element method (SBFEM). These include models for linear and nonlinear, static and dynamic, and single and multiple crack propagation problems, and application to efficient prediction of deterministic size effect laws and complicated fracture behavior of reinforced concrete structures. The advantages and disadvantages of these approaches are compared with the FEM.

A simplified meshless methods for brittle fracture and nonlinear material is presented. In this method, the crack is modeled by a set of discrete crack segments crossing the entire domain of influence of the meshless shape functions. The key advantage of this method is its simplicity since no representation of the crack topology is needed. A nonlocal stress tensor around the crack tip is used as fracture criterion. A neo-Hooke material in the bulk material is used and a cohesive zone model is employed once discrete cracks occur. We also present consistent linearization of the cohesive zone model. The method is applied to fracture modeling in concrete that is accompanied by excessive cracking and therefore methods that represent the crack path have major drawbacks. We demonstrate the accuracy of the proposed method for complex problems involving mode-I and mixed mode failure.

The mixed mode (I/II) fracture of concrete is investigated by using a four-point combined discrete and finite elements method. The potential fracture zone is simulated by the discrete elements (DEs) and the other zone by the finite elements (FEs). A cohesive fracture model is employed to simulate the brittle fracture only in the DE subregion. Mesh-size independency of the cohesive fracture model subjected to the DE is carefully investigated with a simple case. Subsequently, the mixed mode fracture behaviors of two simple concrete specimens are simulated and the simulation results achieve good agreements with the other simulations and experimental results.

Concrete is a typical multiphase composite material in which the initiation and propagation of cracks under fatigue load are mainly determined by its mesoscopic structure. In this paper, a concrete multiphase mesoscopic model which considers thickness of interfacial transition zone (ITZ) varying with aggregate’s size is established by the integrated scripting method. The model comprehensively contains the stochastic characteristics of concrete mesoscopic structure. According to the fatigue crack propagation characteristics in different stages, a multiscale method is proposed by establishing the interactive mesoscopic and macroscopic models to targetedly analyze the whole process of fatigue crack initiation, propagation and failure of concrete specimen. Based on the technique of cycle block, concurrent simulation of concrete damage and crack propagation under high-cycle fatigue load is realized. The analysis results show that fatigue cracks in concrete mainly born near the ITZ and gradually enter into the cement mortar matrix to formulate the cracks with finite size. These cracks influence each other until the dominant crack appears and insatiably propagates to result in the failure of specimen.