Search results

The purpose of this paper is to investigate the effect of elevated temperature on mechanical and physical properties of concrete specimens obtained by substituting the river sand with copper slag (CS) at proportions of 25%, 50%, 75% and 100%. The specimens were heated in an electric furnace up to 100, 200, 300, 400, 500 and 600 C and kept at these temperatures for 2 h duration. After the specimens were cooled in the furnace, mass loss, ultrasonic pulse velocity (UPV), compressive strength, split tensile strength (STS), flexural strength (FS) and modulus of elasticity (MOE) values were determined. No spalling occurred in the specimens after subjected to elevated temperature. The surface cracks were observed only in specimens exposed to 600 C. The maximum reduction in compressive strength and STS at 600C is 50.3% and 36.39% for referral mix (NC), 18% and 16% for specimens with 100% CS (MCS4). The reduction in MOE of specimens is observed to be high as copper slag content increases with increasing temperature. Scanning electron microscopy (SEM) studies are carried out to examine the changes in micro-structures of specimens after exposed to elevated temperatures.

After casting of concrete specimens, it is cured for 28 days. After attainment of 28 days age, the concrete specimens is taken out from the curing tank and allowed to dry for 2 days to remove any moisture content in the specimens to prevent explosive spalling during the time of heating. The prepared concrete specimen is subjected to temperatures of 100^°C, 200^°C, 300^°C, 400^°C, 500^°C and 600^°C up to 2 h duration. The physical test, mechanical test and SEM studies are carried out after cooling of specimens to room temperature (RT). The quality of concrete specimens is measured by conducting UPV test after cooling to RT.

The post-thermal strength properties of concrete specimens with copper slag contents are higher than referral mix concrete. The reduction of MOE of concrete specimens is more with incremental in copper slag content with increase in temperatures. Furthermore, the quality of concrete specimens is ranging from “good to medium” up to 500C temperatures based on UPV test.

In this research work, the natural sand is fully replaced with copper slag materials in the concrete mixes. The post-thermal strength properties like residual compressive strength, residual STS, residual FS and residual MOE is higher than referral mix after subjected to elevated temperature conditions. Higher density and toughness properties of copper slag materials will contribute to concrete strength. The effect of elevated temperature is more on MOE of concrete specimens having higher copper slag contents when comparing to specimens compressive strength.

Pipe cooling is an important measure for controlling the temperature in mass concrete. Since the temperature field in mass concrete containing cooling pipes is unsteady and three‐dimensional, and there are huge quantities of the cooling pipes in the concrete, the study of efficient and reliable algorithm is crucial. The purpose of this paper is to develop the composite element method (CEM) for the temperature field in mass concrete containing cooling pipes.

Each cooling pipe segment is looked at as a special sub‐element having definite thermal characteristics, which is located explicitly within the composite element. By the variational principle, the governing equation for the composite element containing cooling pipes is established.

One of the remarkable advantages of the method proposed is that each cooling pipe can be simulated explicitly while the difficulty of mesh generation around cooling pipes can be avoided.

The paper demonstrates how composite elements containing cooling pipes are degenerated to the conventional finite elements automatically when the first stage artificial cooling finished, and conversely, the conventional finite elements can also be transformed to the composite elements automatically when the second stage artificial cooling started. The comparison of the numerical example using FEM and CEM shows the rationality of the proposed method.

This paper aims to present the results of testing of low-strength concrete specimens exposed to elevated temperatures. These data are limited in the existing literature and do not exist in Pakistan.

An experimental testing programme has been employed. Cylindrical specimens of 100 × 200 mm were used in the testing programme. These were heated at temperatures which were varied from 100°C to 900°C in increment of 100°C. Similar specimens were tested at ambient temperature as control specimens. The compressive and tensile properties of heat treated specimens were determined.

The colour of concrete started to change at 300°C and hairline cracks appeared at 400°C. Explosive spalling was observed in few specimens in the temperature range of 400°C-650°C which could be attributed to the pore pressure generated by steam. Significant loss of concrete compressive strength occurred on heating temperatures larger than 600°C, and the residual compressive strength was found to be 15 per cent at 900°C. Residual tensile strength of concrete became less than 10 per cent at 900°C. The loss of concrete stiffness reached 85 per cent at 600°C. Residual Poisson’s ratio of concrete increased at high temperatures and became nearly six times larger at 900°C as compared to that at ambient temperature.

The parameters of the study included heating temperature and effects of temperature on strength and stiffness properties of the concrete specimens.

Building fire incidents have increased in Pakistan. As a large number of reinforced concrete (RC) buildings exist in the country, the data related to elevated temperature properties of concrete are required. These data are not available in Pakistan presently. The study aims at providing this information for the design engineers to enable them to assess and increase fire resistance of RC structural members.

The presented study is unique in its nature in that there is no published contribution to date, to the best of authors’ knowledge, which has been carried out to assess the temperature-dependent mechanical properties of concrete in Pakistan.

Polyurethane concrete has a high strength-to-weight ratio in the short term, and the strength-to-weight ratio stage during the maintenance period is critical. Freeze-thaw cycles have a noticeable damaging effect on the durability of polyurethane concrete. The engineering specification of polyurethane concrete with incomplete hydration reaction must be studied, as well as the development of internal structure during curing. In this paper, the polyurethane concrete tests were set up under eight distinct maintenance settings based on the climate features of the northern area and the service environment. The test results were evaluated to determine the effect of the number of early freeze-thaw cycles and the time node of early freeze-thaw cycles on the mechanical characteristics of polyurethane concrete, which revealed that the time node of freeze-thaw damage impacted the freeze-thaw resistance of polyurethane concrete susceptible to early freeze-thaw damage.

The early-age freeze-thaw damage polyurethane concrete was experimentally studied by controlling the time node of the freeze-thaw cycle and the curing environment. The test considered the time node, frequency of freeze-thaw damage of polyurethane concrete and the influence of subsequent curing environment and observed the mass change, relative dynamic elastic modulus, relative durability index, compressive strength and apparent damage of polyurethane concrete. The early mechanical properties of polyurethane concrete were studied by analyzing the change of numerical value. The microscopic mechanism of strength formation of polyurethane concrete was analyzed by XRD, FTIR and SEM image.

The closer the time of freeze-thaw damage was to the specimen hardening, the worse the mechanical properties and structure were, according to SEM photographs. For specimens with serial number of 12-groups, its compressive strength is only 82.39% of that of the standard group, even if the curing process continues after 20 times thawing, which increased early environment exacerbate strength loss in polyurethane concrete and also reduced freeze-thaw resistance. The findings of the tests reveal that curing can restore the freeze-thaw resistance of damaged polyurethane concrete. Curing in water has a better recovery impact than curing in air; the mechanical properties can be restored by sufficient re-curing time and good re-curing conditions.

By studying the freeze-thaw cycle test and test results of polyurethane concrete in different curing time nodes, the relationship between the mechanical properties of polyurethane concrete and the time node, number of freeze-thaw cycles, and subsequent maintenance environment was explored. Considering the special mechanism of strength formation of polyurethane concrete, the polyurethane concrete damaged by freeze-thaw has the ability to continue to form strength under subsequent maintenance. This experimental study can provide an analytical basis for the strength formation and reconditioning of polyurethane concrete structures subjected to freeze-thaw environments during the curing time under extreme natural conditions in fall and winter in actual projects.

Concrete is a widely used construction material which can be prepared using locally available resources (aggregates, cement and water) by following relevant standard guidelines. The residual properties of concrete determined by heating in an electric furnace may not produce a similar effect of fire. The purpose of this paper is to compare the effect of a fire with that coming from the exposure of normal strength concrete to predetermined reference temperatures, for which two sets of specimens were heated in a fire furnace provided with gas burners and an electric furnace.

The concrete cubes and cylinders were subjected to 200^oC, 400^oC, 600oC and 800^oC temperature in a gas-controlled fire furnace and an electric furnace for 2 h. The physical properties and mechanical properties of concrete were determined after cooling the specimens in air. The quality of concrete specimens was determined using the ultrasonic pulse velocity test, and surface hardness of the heat-exposed cubes was recorded using the Schmidt rebound hammer.

The fire-exposed specimens were found to have lower residual compressive strength, tensile strength and higher porosity/voids/internal cracks than the specimens heated in an electric furnace at the same temperature. Further, a good agreement with compressive strength and rebound numbers was observed for each of the two heating systems (flames coming from gas burners and electric furnace).

Normal strength concrete specimens exposed to heat in an electric furnace will not give the same effect of fire having the same maximum temperature. Further, it is noticed that concrete subjected to elevated temperature is sensitive to heating modalities, be it the flames of a gas furnace or the radiation of an electric furnace.

Fire can severely affect concrete structures and with knowledge of the properties of materials, the damage can be assessed. Aggregate, cement matrix and their interaction are the most important components that affect concrete behaviour at high temperatures. The effect of incorporating recycled concrete aggregate or cementitious materials, namely, cement type and pulverized fly ash, are reviewed to provide a better understanding of their involvement in fire resistance.

More investigation research is needed to understand the fire resistance of such sustainable concrete that was already constructed. The present study illustrates the effect of using recycled concrete aggregate and cementitious materials on the fire resistance of concrete. To do so, a literature review was conducted and relevant data were collected and presented in a simple form. The author's selected research findings, which are related to the presents study, are also presented and discussed.

Recycled concrete aggregate enhances the concrete behaviour at high temperatures when it substitutes the natural aggregate by reasonable substitution (more than 25–30%). It also almost eliminates the possibility of spalling. Moreover, utilizing both supplementary cementitious materials with recycled concrete aggregate can improve the fire resistance of concrete. The incorporation of pulverized fly ash and slag in Portland cement or blended cement can generally keep the mechanical properties of concrete at a higher level after heating to a high temperature.

Recycled concrete aggregate enhances the concrete behaviour at high temperatures when it substitutes the natural aggregate by reasonable substitution (more than 25–30%). It also almost eliminates the possibility of spalling. Moreover, utilizing both supplementary cementitious materials with recycled concrete aggregate can improve the fire resistance of concrete. The incorporation of pulverized fly ash and slag in Portland cement or blended cement can generally keep the mechanical properties of concrete at a higher level after heating to a high temperature.

Concrete is the most basic of building materials and yet, in the hands of the expert, is capable of providing strength, durability and even elegance far in excess of many of its manufactured competitors. The technology is by now well established but the production of concrete of a consistently good quality is by no means simple.

Societal needs produce infrastructural demands that often, require innovative industrial solutions to optimally satisfy them. One such need is fresh clean water and this has been met in part, by a global infrastructure of dams and reservoirs. Dams have borne witness to their innovative construction design, technology and management (CDTM) over the years and the purpose of this paper is to examine an example of this, relating to Claerwen dam in Great Britain.

The study used historical case study method based on Busha and Harter's (1980) model, to accommodate synthesis of extant, historical and archive data. Subsequent archival data analysis is founded predominately on document synthesis and embraces a longitudinal character.

Benefiting incontrovertibly from industrial innovations, Claerwen was constructed in markedly different ways from its “sister” phase 1 Elan Valley dams built 50 years earlier, to uniquely combine vernacular aesthetic with contemporary CDTM of the time and create a reservoir with capacity almost equal to that of the entire phase 1 dams combined.

Findings offset a dearth of historical construction research more generally; and that relating to dam infrastructure, more specifically.

Minimal literature exists regarding innovations in British dam building so the study is especially original in that respect.

The durability of concrete containing recycled aggregates, sourced from concrete specimens that have been tested in laboratory testing facilities, remains understudied. This paper aims to present the results of experiments investigating the effect of incorporating such type of concrete waste on the strength and durability-related properties of concrete.

A total of 77 concrete cylinders sized Ø100 × 200 mm with varying amount of recycled concrete aggregate (RCA) (0%–100% by volume, at 25% increments) and maximum aggregate size (12.5, 19.0 and 25.0 mm) were fabricated and tested for slump, compressive strength, sorptivity and electrical resistivity. Disk-shaped specimens, 50-mm thick, were cut from the original cylinders for sorptivity and resistivity tests. Analysis of variance and post hoc test were conducted to detect statistical variability among the data.

Compared to regular concrete, a reduction of slump (by 18.6%), strength (15.1%), secondary sorptivity (31.5%) and resistivity (17.0%) were observed from concrete containing 100% RCA. Statistical analyses indicate that these differences are significant. In general, an aggregate size of 19 mm was found to produce the optimum value of slump, compressive strength and sorptivity in regular and RCA-added concrete.

The results of this study suggest that comparable properties of normal concrete were still achieved by replacing 25% of coarse aggregate volume with 19-mm RCA, which was processed from laboratory-tested concrete samples. Therefore, such material can be considered as a potential and sustainable alternative to crushed gravel for use in light or nonstructural concrete construction.

The purpose of this paper is to present the construction process innovations that enabled the successful delivery of the hybrid mass timber high-rise building in Canada, the Brock Commons Tallwood House at the University of British Columbia. It is one of a set of papers examining the project, including companion papers that describe innovations in the mass timber design process and the impact of these innovations on construction performance. The focus of this paper is on innovation in the construction phase and its relationship to innovations implemented in previous project phases.

A mixed-method, longitudinal case study approach was used in this research project to investigate and document the Tallwood House project over a three-year period. Both quantitative and qualitative data collection and analysis techniques were used. Members of the research team observed prefabrication and construction, conducted periodic interviews and reviewed project artefacts.

The research identified three innovation “clusters,” including the use of innovative tools, techniques and strategies in the design and construction processes and the role they played in delivering the project. The “clusters” were further characterized according to the type of “connectivity” they afforded, either facilitation, operationalization or materialization. These two perspectives support a compounding view on innovation and help to understand how it can flow throughout a project’s life cycle and across its supply chain. Three process-based innovations were initiated during the design phase, integrated design process, building information modeling and virtual design and construction and flowed through to the construction phase. These were seen to enable the creation of connections that were crucial to the overall success of the project. These innovations were operationalized and enacted through the construction phase as design for manufacturing and assembly and prefabrication, staged construction and just-in-time delivery, integration of safety and risk management and a rigorous quality control and quality assurance process. Finally, a full-scale mock-up was produced for practice and constructability assessment, materializing the radical product innovation that was the mass timber structure. These strategies are used together for a synergistic and integrated approach to increase productivity, expedite the construction schedule and develop an innovative building product.

This paper details an in-depth investigation into the diffusion dynamics of multiple systemic innovations for the construction process of a unique building project, the tools and techniques used by the construction manager and team, and the challenges, solutions and lessons learned.