Concrete Test Block Research Articles

Preparation of concrete from vitrified slag: process parameter optimization and characterization

ABSTRACT Vitrification is the safest and most effective method for treating solid waste incineration residues, and the utilization of vitrified slag can promote recovery of waste resources. By using the response surface methodology to comprehensively consider the impact of three factors – cement substitution ratio, water-binder ratio, and sand rate – on the strength of concrete, the optimal process parameters for predicting the maximum 28-day compressive strength of concrete specimens are determined as follows: 5% cement substitution ratio, 0.69 water-binder ratio, and 40% sand rate. The experiments demonstrate that concrete specimens prepared by partially replacing cement with molten glass slag exhibit excellent mechanical and physicochemical properties. As the curing age increases, the compressive strength of the specimens also enhances. Leaching test results showed that the concrete test block met groundwater Class III quality standards, and the addition of vitrified slag powder reduced the content of calcium hydroxide and improved concrete performance.

Theoretical Investigation on Indirect Tensile Strength of Concrete with Rectangular Cross-Section under Locally Distributed Load.

The indirect tensile test plays a crucial role in experimental investigations of brittle material properties. In this study, a mechanical analysis model of the rectangular test block is established based on the theory of elastic mechanics for the characteristics of the indirect tensile test. The theoretical solution of the triangular series is derived for the rectangular test block under the locally distributed load. The finite element simulation results and splitting test results were compared with the theoretical results. The results of the study verify the accuracy of the theoretical solutions. Based on the proposed analytical solution, the effects of loading width and length-to-height ratio (h/l) of local loading on the measured tensile strength of test block are discussed. The results demonstrate that the tensile strength of the test block increases as the loading width expands, and the rate of growth in the recorded tensile strength gradually stabilizes. The variation in loading width affects the location of crack initiation points during the concrete test block splitting tests. When the loading width exceeds 6% of the side length of test block, the cracking point is positioned at the center of test block, ensuring the effectiveness of the splitting test. As the length-to-height ratio of the test block increases, there is a general upward trend in the measured tensile strength. When h/l < 0.6, the measured tensile strength initially increases before decreasing. However, when h/l > 0.6, the measured tensile strength consistently increases, with the rate of increase gradually diminishing until it stabilizes. The length-to-height ratio also significantly influences the location of the cracking point in the test block. As the length-to-height ratio increases, the cracking point initially shifts from around the center to the central point and then further from the center toward the edge. To ensure that the location of the crack initiation point is in the center of the specimen and that the tensile strength is close to the measured result, the length to height ratio can be chosen at around 0.85.

Simulations and experimentation of ultrasonic wave propagation and flaw characterisation for underwater concrete structures

ABSTRACT Ultrasonic non-destructive evaluation of concrete submerged in water is a complex phenomenon that has important implications for the durability and safety of marine structures such as bridges, piers and offshore platforms. The scattering of ultrasonic waves inside concrete materials with aggregate size comparable to the ultrasound wavelength often limits the interpretation of inspection results. To enhance the understanding of ultrasonic wave propagation inside the underwater concrete, numerical simulations using the finite element method (FEM) with the Transient Acoustics-Piezoelectric Interaction application mode of Multiphysics software package have been developed. This study focuses on developing a 2D numerical model to reproduce and illustrate the propagation of ultrasound in seven types of underwater concrete test blocks with various types of inclusions and voids embedded inside it. The B-Scan 2D images of the concrete test blocks were acquired using the simulated data and compared with experimental results acquired using an in-house developed four-channel ultrasonic imaging system. Both simulation and experimental results showed a good resemblance, indicating that B-Scan imaging can be applied to identify and characterise various types of defects and inclusions in underwater concrete structures, providing better assessment of the material than conventional ultrasonic pulse velocity (UPV) method.

Research on improving the durability performance of damaged concrete based on ultra high performance concrete repair

AbstractThis article uses ultra‐high performance concrete (UHPC) to repair damaged concrete and analyzes the durability performance of the repaired concrete. Among them, three erosion solutions with a mass concentration of 2.8% NaCl + 0.29% Na2SO4, 5% NaCl, and 5% NaCl + 10% Na2SO4 were designed to soak the concrete specimens for 1 to 3 months. Taking the SWC test group as an example, when the concrete test block undergoes 30 dry wet cycles and the erosion depth is 20 mm, the difference in chloride ion concentration under different diffusion dimensions is not significant. After 90 dry wet cycles, at a depth of 20 mm, the chloride ion concentration inside the concrete in the three‐dimensional diffusion state reached 3 times that of one‐dimensional diffusion, and the chloride ion concentration in the two‐dimensional diffusion state also reached 2 times that of one‐dimensional diffusion. At a depth of 30 mm, a small amount of chloride ion content was also found in the two‐dimensional diffusion and three‐dimensional diffusion.

Study on Flexural Strength of Interface between Full Lightweight Ceramsite Concrete and Ordinary Concrete

The efficacy of full lightweight ceramsite concrete as a restorative material has been widely acknowledged, given its light weight, strength, and durability. However, the extent of its performance in repairing existing or old concrete remains uncertain. This study examined the reparation of flexural performance with full lightweight ceramsite concrete, using 14 different combinations of old and new concrete test blocks. The primary focus of the study was on investigating the flexural bond strength of the interface between the old and the new concrete. This included understanding the effects of the interfacial roughness, interfacial agent type, and concrete curing age of the concrete on the flexural strength. The test results showed that increasing the interface roughness from 0 mm to 5 mm resulted a restoration of the flexural strength of the sample by approximately 59%. Additionally, the flexural strength of the specimens was restored by 62%–78% of their original strength with the application of different types of interfacial agent. To rank the impact of these factors on the flexural strength, a univariate analysis of variance was conducted. This allowed us to establish a mathematical formula for calculating the flexural capacity of old and new concrete interfaces, taking the three aforementioned factors into account.

6 Characterization of Aerosolized Particles Generated During Cutting of Carbon Nanotubes-Embedded Concrete

Abstract Engineered nanomaterials are revolutionizing many industries, but little is known about potential exposures during the life cycle of nano-enabled composites. This study was conducted to characterize aerosolized particles using direct-reading instruments and integrated air samplers during cutting multi-walled carbon nanotubes (MWCNT)-embedded concrete cylinder blocks. Three types of blocks, 0% (reference), low%, and high% MWCNT, were tested in a specially designed enclosure housing an apparatus for the cutting of a block with an automated computer-controlled process. The highest particle number concentration (163,821 particles/cm3) was measured for the reference cylinder, while others showed similar concentrations (131,689 particles/cm3 and 140,954 particles/cm3 for the low% and high% blocks, respectively). Regardless of the cylinder type, the size-selected particle number concentrations revealed one main mode with a peak at 0.72 µm indicating no shift in the size distribution from addition(s) of MWCNT. Respirable mass concentrations were 342 mg/m3, 405 mg/m3, and 432 mg/m3 for the reference, low%, and high% blocks, respectively. The mass median aerodynamic diameters were similar, 5.23 µm for the reference and 5.05 µm for both low% and high% blocks, indicating a predominant respirable fraction. Respirable particles (quartz, feldspar, paste, etc.) often appeared to be agglomerated materials that included both paste and aggregate minerals. No free MWCNT were observed by electron microscopy from low% and high% samples. These initial studies found no evidence of free MWCNT by cutting concrete test blocks and only minor differences in the particulate aerosol generated, which included a general increase in respirable mass with increasing % CNT.

Heavy concrete shielding properties for carbon therapy

As medical facilities are usually built at urban areas, special concrete aggregates and evaluation methods are needed to optimize the design of concrete walls by balancing density, thickness, material composition, cost, and other factors. Carbon treatment rooms require a high radiation shielding requirement, as the neutron yield from carbon therapy is much higher than the neutron yield of protons. In this case study, the maximum carbon energy is 430 MeV/u and the maximum current is 0.27 nA from a hybrid particle therapy system. Hospital or facility construction should consider this requirement to design a special heavy concrete. In this work, magnetite is adopted as the major aggregate. Density is determined mainly by the major aggregate content of magnetite, and a heavy concrete test block was constructed for structural tests. The compressive strength is 35.7 MPa. The density ranges from 3.65 g/cm3 to 4.14 g/cm3, and the iron mass content ranges from 53.78% to 60.38% from the 12 cored sample measurements. It was found that there is a linear relationship between density and iron content, and mixing impurities should be the major reason leading to the nonuniform element and density distribution. The effect of this nonuniformity on radiation shielding properties for a carbon treatment room is investigated by three groups of Monte Carlo simulations. Higher density dominates to reduce shielding thickness. However, a higher content of high-Z elements will weaken the shielding strength, especially at a lower dose rate threshold and vice versa. The weakened side effect of a high iron content on the shielding property is obvious at 2.5 μSv/h. Therefore, we should not blindly pursue high Z content in engineering. If the thickness is constrained to 2 m, then the density can be reduced to 3.3 g/cm3, which will save cost by reducing the magnetite composition with 50.44% iron content. If a higher density of 3.9 g/cm3 with 57.65% iron content is selected for construction, then the thickness of the wall can be reduced to 174.2 cm, which will save space for equipment installation.

Model test analysis of control effect of building foundation elastic pad on subway environmental vibration

Building foundation elastic pad is one of the important measures for subway vibration control. In order to understand the subway vibration control effect of elastic pad on superstructure, two identical concrete test blocks were poured on site near a subway line. Taking the real subway vibration load as the input source strength, the vibration isolation effect of elastic pad on upper concrete mass block was compared and analyzed; At the same time, the influence of the backfill around the underground foundation of the building on the vibration isolation effect is simulated and analyzed. The backfill has a non negligible restraint effect on the building, improves the vertical natural frequency of the "building elastic pad" system, and then reduces the vibration isolation effect of the elastic pad. Therefore, it is very necessary to lay the elastic pad on the side wall around the building to reduce the lateral restraint effect of the backfill.

Experimental Study on the Properties of Mixed-Fiber Concrete Shield Tunnel Segments Subjected to High Temperatures

In order to study the mechanical and damage behavior of concrete shield tunnel segments under a high temperature, two self-compacting concrete and three mixed-fiber (steel and polypropylene fiber) self-compacting concrete test blocks were designed. The influence of several key factors, including fire duration, pre-loading, and concrete type, on the fire behavior of concrete shield tunnel segments were studied. The results show that the type of fiber and pre-loading have an important influence on crack development in concrete shield tunnel segments. Compared with undoped segments, cracks in segments with steel fibers and polypropylene fibers appeared later, and the average crack spacing decreased. The pre-loading has an important effect on the vertical deformation before and after the temperature rise. As the load level increases, so does the deformation after the temperature rise. The influence of the initial load level should be considered when designing the fire resistance of the segment.

Ultrasonic Imaging of Concrete/ RCC Structures using Immersion Technique

There has been a rapid increase in the construction of under-water concrete structures all over the world and the maintenance and rehabilitation of these concrete structures pose a major concern for estimating the quality and the useful remaining life of these structures. To cater to such needs, the detection of defects, porosities and rebar locations inside the Concrete/Reinforced Cement Concrete (RCC) structures have been carried out using the in-house developed single-channel ultrasonic imaging system at Electronics Division, BARC, India. Commercially, the inspection of under-water concrete structures is being carried out by utilizing Ultrasonic Pulse Velocity (UPV) method in Transmit-Receive (T-R) mode to indirectly estimate the density and strength of the concrete structure under test. UPV method requires a skill to interpret the data provided by the UPV instrument. The in-house developed single-channel system can perform imaging of Concrete/ RCC structures both in Pulse Echo (PE) as well as in T-R mode and can function in UPV mode. The imaging system performs data acquisition and temporal averaging of the RF bipolar data to achieve high Signal-to-Noise Ratio (SNR) ( &gt; 20 dB). In this paper, different types of concrete blocks with simulated defects and RCC blocks with steel rebars have been utilized for the inspection using the single-channel imaging system in water-immersion mode. The B-Scan images have been acquired for the concrete and RCC sample test blocks, using 54 KHz water immersion transducer in PE mode. The acquired B-Scan images have revealed the internal details of the Concrete and RCC sample test blocks, resembling the defects generated in the test blocks. The A-Scan waveform was also acquired on the 1 metre thick concrete block in contact PE mode, which shows the capability of the single channel ultrasonic imaging system for the inspection of such thick concrete blocks.

Laser Sensing System for Contactless Detection of Subsurface Defects in Concrete Tunnel Lining

Regular inspections of underground infrastructure are mandatory to maintain structural integrity and traffic safety. Standard procedures rely on visual inspection, complemented by testing for internal defects of the tunnel lining with the hammering method. This testing method uses manual excitation with a hammer and interpretation of the perceived sound by an engineer or technician. Result quality is based on the experience of the executing personal and thus highly subjective. The presented project aims at the automation of this procedure to enable a fast and objective inspection covering the whole tunnel lining. To achieve this, a new laser-based measurement system for detecting near surface defects in large concrete structures is developed. Surface vibrations are induced with plasma ignition and measured with a Doppler Vibrometer. The system has motorized mirror adjustment and can thus obtain fast-paced measurements on a grid. We present the experimental setup, the measurements performed on a concrete test block with artificial defects and the algorithms for automated defect detection. From the measured eigenfrequencies, we derive the size and location of defects. Computer vision techniques are adapted to make the system resilient against variable environmental conditions, like noise and temperature, or changes in construction material and age. These sophisticated signal processing methods are applied to extract relevant information from the measurements and are combined with topological data to provide service personnel with detailed maps for maintenance work.

Study on Ultrasonic Nondestructive Testing of Self-Compacting Concrete under Uniaxial Compression Test.

To study the variation law of ultrasonic parameters of self-compacting concrete before and after damage under uniaxial compression test conditions, the C30 self-compacting concrete blocks stored for 7 days and 28 days were subjected to ultrasonic nondestructive testing, and the variation law of the sound time, amplitude, and sound velocity before and after the damage of self-compacting concrete blocks was emphatically analyzed. The concrete acoustic detection software was introduced to judge and analyze the abnormal values of the parameters of each measuring point, and the defect distribution map of each test block was obtained. The results showed that after curing the self-compacting concrete test block for 7 days and 28 days, the average value of sound time before and after the failure of each measuring point of the test block is small, and the average value of sound time before the failure is less than that after; the average amplitude after failure is smaller than that before failure, and the amplitude of some measuring points will be smaller than that before. The average sound velocity after failure is less than that before failure, and the internal defects appear and the structure is not dense. This study provides a theoretical basis for the application of ultrasonic detection technology in the field of self-compacting concrete and also provides a practical basis for the stability monitoring and failure warning of self-compacting concrete.

Data analysis of the long-term residual effect of cathodic protection on reinforced concrete structures

The application of impressed current cathodic protection (CP) is a well-established technology for the corrosion protection of reinforced concrete structures situated in marine environments. While the protective benefits of cathodic protection are well known, the lasting effects following the discontinuation of CP current are not entirely understood. This paper presents research findings on the residual protective effect which is known to occur following long durations of impressed current cathodic protection. The residual effect was replicated in university laboratories using reinforced concrete test blocks and accelerated CP testing methods. The experimental results depicted a clear improvement in the electrochemical state of the reinforcing steel with a shift of 150 to 300 mV to more positive values following CP application. The research also involved analysis of monitoring data from six in-service cathodic protection systems which were operating in Australia for nearly two decades. The behaviour of the steel potential readings was analysed and the results of the combined research confirmed that the protection provided by cathodic protection systems does not actually cease when the CP current is switched off. Rather, the embedded steel undergoes a significant and sustained shift to more positive values and this phenomenon is documented and discussed in this paper.

Modeling study on the influence of nano admixture on the strength of high-rise building concrete

To solve the problem of high prediction error of concrete strength in traditional methods, a modelling method of the influence of nano admixtures on the strength of high-rise building concrete is proposed. UHPC concrete was selected as the test object to prepare different test blocks. Establish the concrete strength prediction model based on RBF network, optimise the prediction model, obtain the multivariate nonlinear model, input the material preparation data of nano admixture into the model, output the concrete strength prediction results, and complete the analysis of the impact of nano admixture on concrete strength. The test results show that the compressive strength of concrete reaches the best when the nano content is 1%; When the content of nano admixture is 30%, the flexural strength of concrete is the best; When using this method to predict the strength of concrete test block, the minimum prediction error is only 0.5%.

Embedded system for ultrasonic imaging of under-water concrete structures

Many of the modern concrete structures such as sea-links and bridges are built in water. They require structural health monitoring (SHM) and audit to ascertain the quality and estimation of remaining useful life. To meet these requirements, a single-channel ultrasonic imaging system has been designed and developed to detect defects, porosities and rebar locations inside the Concrete/ Reinforced Cement Concrete (RCC) structures. This real-time and reconfigurable embedded system whas evaluated by carrying out under-water imaging of Concrete and RCC test blocks. Conventionally, Ultrasonic Pulse Velocity (UPV) method is being utilized over three decades in Transmit-Receive (T-R) mode to estimate the density and strength of the concrete structure under test. UPV method requires a skill to interpret the data provided by the UPV instrument. The novelty of the single-channel system discussed in this paper is that it is capable of inspecting Concrete/ RCC structures both in Pulse Echo (PE) as well as in T-R mode. An application software has been developed using C# in a visual environment for image acquisition and the control of Data Acquisition (DAQ) hardware has been interfaced to the computer via USB. The imaging system performs data acquisition and coherent averaging of the RF bipolar data to achieve Signal-to-Noise Ratio (SNR) higher than 20 dB. The performance of the system was evaluated by acquiring B-Scan images of the water submerged concrete test blocks having Side Drilled Hole (SDH) and RCC blocks with one as well as two steel rebars, using 54 kHz water immersion transducer in PE mode. The acquired B-Scan images have revealed the internal details of the sample test blocks, resembling the defects generated in the test blocks. High voltage tone burst bipolar pulser with maximum output of (± 350 V) has been specifically designed for this system to inspect highly attenuative porous and non-homogeneous Concrete/ RCC materials for the detection of SDH and reinforced steel bars in the concrete test blocks, using B-Scan imaging technique.

Experimental research on cyclic impact load of concrete during curing period

In order to study the influence of cyclic impact load on the compressive strength of concrete during the curing period, we used a self-made drop-weight impact test device to conduct a daily impact test on C40 concrete specimens with a curing period of 28 days. At the same time, the longitudinal wave velocity test of the test block before and after the impact was carried out, and the 28-day uniaxial compressive strength of the concrete test block was finally measured. The results show that the cyclic impact load during the curing period will cause internal damage to the concrete, and the uniaxial compressive strength is significantly reduced; the acoustic wave test results show that the damage of the concrete under the impact energy of 11.76kJ, 5.88kJ, 7.84kJ, and 8.82kJ is 0.035, 0.022, 0.031, 0.031. The uniaxial compressive strength values after 28 days decreased by 11.93, 4.68, 7.6, 10.23 MPa. There is a positive correlation between impact load, damage and reduction in compressive strength.

Basic test of mix proportion of foamed concrete with aluminum powder as foaming agent

In this paper, the method of producing bubbles by the reaction of aluminum powder and sodium hydroxide is used to make foam concrete test blocks and test their expansion rate and compressive strength. The foamed concrete was made through experiments of controlling the amount of cement, water and the relative content of aluminum powder, and the best mix ratio was selected from the comparative analysis of the compressive strength of 7d, 14d and 28dconcrete. Experimental results: The amount of cement and the water-cement ratio and the relative content of aluminum powder have a significant impact on the compressive strength and expansion rate. Conclusion: Starting from the ratio of the relative content of aluminum powder in foamed concrete to the amount of cement, the analysis of compressive strength and expansion rate provides a theoretical basis for the future study of its mix ratio, which greatly shortens the test time and saves costs.

Influence of Aluminum Powder Content on Expansion Rate of Foamed Concrete

Foamed concrete is a heat preservation and noise reduction material made of cement and aluminum powder as foaming agent. The experiment mainly studies the influence of different water-cement ratio, foaming agent dosage and cement dosage on the expansion rate of foamed concrete test block. The experimental results show that when the water-cement ratio increases from 0.4 to 0.6, the expansion rate decreases gradually. When the content of aluminum powder foaming agent increased from 0.05% to 0.40%, the expansion rate showed a trend of “increasing first and then decreasing”. When other conditions are the same, the expansion rate of cement increases from 500kg/m3 to 800kg/m3, showing a trend of “decreasing first and then increasing”.

Theoretical Study on the Size Effect of the Rate Characteristics of Concrete Cubes Compressive Strength

In order to study the effect of size effect and rate correlation on the mechanical properties of concrete, a total of 228 concrete cube test blocks of three sizes (70, 100 and 150mm) were tested and studied under four strain rates (10−5,10−4,10−3,10−2/s). The test results show that under the same strain rate, the peak stress of concrete decreases with the increase of the size. Under the same size, the peak stress of concrete increases with the increase of strain rate. Experimental data were used to verify and modify Weibull size effect equation based on statistics and Bazant size effect equation based on fracture mechanics. The experimental data fit well with the equation, and the size effect theory of concrete strength with correlation of holdup is established.

Application of HCSA expansive agent in crack control of mass concrete

The open section of the west artificial island of the Hong Kong-Zhuhai-Macao Bridge is a mass concrete structure. The concrete was poured in two times in the vertical direction, that is, the whole bottom plate was poured in the first time, and the middle wall and two side walls were poured in the second time. The side wall and middle wall are easy to crack due to the long time interval between two concrete castings. In order to study the function and effect of HCSA expansion agent in the crack control of mass concrete, the applicable condition of compensating shrinkage in the crack control of mass concrete is analyzed first. Then the effect of HCSA expansion agent was studied in laboratory and field. The experimental results show that HCSA expander has a good expansion effect under laboratory conditions, but it has no expansion effect on the middle side of the mass concrete test block in the engineering site, instead, it will further increase the internal temperature rise of concrete and increase the shrinkage strain of concrete. HCSA expander is helpless for crack control of mass concrete.