Precast Concrete Industry Research Articles

Phase change materials sheets for energy-efficient heat curing process: A potential idea and performance evaluation

Many countries experience long cold winter, which delays many in-situ concreting activities. Shifting to precast concrete systems is a common solution to continue and maintain construction progress. However, the heat curing process for precast elements represents a challenge for the precast industry due to its high energy consumption (i.e. high fossil fuels dependency and associated high carbon emissions). Therefore, this study examines the feasibility of utilizing micro-encapsulated phase change materials (MPCMs) to achieve a sustainable curing process. Both direct incorporation of MPCMs in the cementitious mixtures and covering specimens with MPCMs sheets were examined under a simulated heat-curing cycle. Results showed that covering specimens with MPCMs sheet eliminated drawbacks induced by MPCMs direct incorporation (i.e. leakage of paraffin, voids, and loss of function). Moreover, utilizing the MPCMs sheet allowed shortening the heat curing holding period by 50% (i.e. from 10 hrs to 5 hrs) while achieving 96% of the desired strength. Findings confirmed the high potential of using MPCMs sheets to cure, save energy, and boost the precast concrete industry's sustainability level.

Using recycled aggregate concrete at a precast-concrete plant: A multi-criteria company-oriented feasibility study

Numerous test results at laboratory scale confirm the utility of Recycled Aggregate (RA) for the development of concrete that demonstrates durability and adequate in-fresh and mechanical behavior. However, feasibility evaluations of the use of RA in real industrial applications are necessary, before any large-scale industrial application of these products can begin. In this research, the feasibility of producing precast-concrete components containing large amounts of coarse RA at a precast-concrete plant is analyzed. Two Self-Compacting Concretes (SCC) were produced incorporating 0% and 100% coarse RA, respectively, at both laboratory scale (0.08 m3) and industrial scale (2 m3). Work took place at the industrial-scale facilities of a precast-concrete company that was collaborating in this study. Flowability and mechanical behavior were maintained as concrete production volumes increased, and concrete strength even increased after adding coarse RA, due to a careful mix design. However, the durability performance worsened by around 20% when produced at industrial scale, being this worsening higher whether coarse RA was used. A Multi-Criteria Decision-Making (MCDM) analysis, in which the criteria of the precast-concrete company defined the relative importance of each concrete property, showed the feasibility of manufacturing precast-SCC components containing coarse RA for interior usage, whose fundamental requirement is adequate mechanical strength. The results of the MCDM analysis also underlined the lower cost of coarse RA, making its use in SCC components cast with large concrete volumes advisable. Overall, the addition of coarse RA in the precast-concrete industry is recommended in the interests of a greener construction sector.

Evaluation of Characteristics and Building Applications of Multi-Recycled Concrete Aggregates from Precast Concrete Rejects.

The construction industry must meet current environmental requirements, mostly those pertaining to the reduction in construction and demolition waste and the consumption of raw materials. The use of recycled concrete aggregates can be part of the solution, but one question that arises is how many times recyclables can be recycled. This unknown involves other related queries regarding the properties and possible uses of repeated recycled concrete aggregates. This research is derived from the precast concrete industry, where multi-recycling is a pressing need. From good-quality parent concretes, three cycles of recycled concrete aggregates were produced and analysed. The final results are promising due to the good quality of the recycled and multi-recycled concrete aggregates obtained. Not only can they be used in low-level applications (backfilling) as usual, but they can also be used for more demanding purposes, such as graded aggregates, cement-treated road bases and concrete pavements. Their use in structural concrete is feasible, but it will be dependent on the water absorption level and the amount of recycled aggregate substitution. This research proves the viability of multi-recycled concrete aggregates with all of the associated environmental benefits.

Enhancing class F fly ash geopolymer concrete performance using lime and steam curing

BackgroundProducing fly ash geopolymer concrete (FGPC) which can be cured by air, water, or steam instead of thermal curing without decreasing its mechanical properties will facilitate using FGPC in cast-in situ applications and precast concrete industry. Furthermore, it will decrease the consumed energy in FGPC production. This research attempts to achieve this goal by investigating the efficacy of supplementing class F FGPC with lime while using different curing processes to generate lime-fly ash geopolymer concrete (L-FGPC) that could be a feasible alternative to ordinary FGPC.MethodsThe studied variables included lime content, molarity of sodium hydroxide (NaOH), additional water content, curing type, and moisture of aggregates. The comparative criteria were setting times of fresh concrete, mechanical properties of hardened concrete, and voids ratio. SEM and X-ray diffraction tests were used to validate test results.ConclusionsSteam curing generated the best mechanical properties of L-FGPC. Using 2% lime content with steam-cured L-FGPC yielded proper setting times and the best mechanical properties. Microstructure tests revealed compact microstructure and decreased voids ratio upon using 2% lime content in L-FGPC. Increasing molarity of NaOH, decreasing additional water content, and decreasing moisture of aggregates enhanced L-FGPC’s mechanical properties.

Evaluation of the Prediction and Durability on the Chloride Penetration in Cementitious Materials with Blast Furnace Slag as Cement Addition

Blast furnace slag (BFS) is a mortar additive in which the utilization of varied curing conditions and the basicity of BFS determine the fineness of the resulting mortar and, thereby, its salt prevention properties. This study evaluates and compares the salt-prevention properties of mortar prepared by either steam curing or water curing. The physical properties, for example, the BFS fineness, revealed the factors significantly affected by basicity that influence the salt-preventive properties of mortar in the specimens examined, such as the lead time and diffusion coefficient. Furthermore, these factors were also significantly affected by differences in curing conditions and other physical properties. However, few studies have examined its use in reducing chloride ion permeability as the main factor of corrosion reactions. Thus, this study evaluates specific surface, water/binder ratio (W/B), and curing conditions on the chloride penetration in cementitious materials with blast furnace slag as cement addition in terms of delaying chloride ion penetration, which affects corrosion reactions. Results of the study are intended to guide development of products for use in the precast concrete industry, toward extending the life of concrete structures, especially reinforced concrete structures in marine environments. In addition, the resulting durability measurements from the experiment conducted are illustrated. This study indicates that differences in Blaine size properties significantly influence water curing. Furthermore, results reveal the effects of combining BFS with various Blaine values and ratio-affecting properties on mortar. In conclusion, concrete materials that decrease durability against chloride attack and improve mechanical properties for precast manufacturer industrial applications are successfully developed in this study. In addition, the use of water-curing conditions, high Blaine value, high cement replacement ratio, and W/B tend to improve the general mechanical property performance and durability against chloride ion attack.

Evaluation of shear strength of pre-stressed hollow core slab

Pre-stressed hollow core slabs have been largely used in the precast concrete industry. They have also been extensively studied, especially regarding the characterisation of strength against web shear failure. However, in most of the studies reported in the literature, the pre-stressing force acting on the tested slabs was not known and torsional effects influenced the results. This work presents a simple and economical methodology that reduces the torsional effects in the tests, to evaluate the shear strength of pre-stressed hollow core slabs. From longitudinally-cut segments of 210 mm deep hollow core slabs with greased strands, the tensile strength of the concrete used in casting the hollow core slab was determined. From longitudinally-cut slab segments, the effective pre-stressing force was also determined at the time of carrying out the shear strength characterisation test. From these tests, the contribution of the concrete and pre-stressing force to the shear strength of the hollow core slab make up by slipformer machine was isolated and determined. Two failure modes were experimentally characterised from the segments, that is, flexural shear and tension shear failure. From the experimental results, an analytical model is proposed to determine the flexural shear strength of 210 mm hollow core slabs and the tension shear strength of non-pre-stressed concrete. A pre-stressed hollow core slab was also tested to validate the proposed analytical model. Additionally, the pre-stressing force transfer length in the hollow core slab was determined, obtaining a value of 65ϕ. Three databases of experimentally tested hollow core slabs, with depths ranging from 160 mm to 320 mm and a/h ratio equal to 2.5, were used to validate the proposed analytical model. A good estimate of the flexural shear strength of these slabs was obtained.

Study of the influence of using recycled brass fibres from electrical discharge machining process on the physical, thermal and mechanical properties of the resulting mortar

Nowadays, metallic fibre reinforced cementitious composites are widely used on many different construction elements: concrete beds, slabs, precast concrete industry, etc. Fibres reduce the crack generation due to the cementitious composite shrinkage and improves its flexural strength, toughness and durability. If metallic waste materials from the industrial manufacturing sector were used instead of using the commercially available metallic fibres, the energy of both the waste recycling process and the manufacturing of the actual commercial metallic fibres would be saved. This paper studies the use of the waste residual brass fibres generated during the electrical discharge machining process as a reinforcement on mortars. With that in mind, two different fibre types (brass covered steel and recycled brass) on two different mix proportions (0.65% and 1.3% by unit volume of mortar) were added to a self-leveling non-reinforced mortar taken as a reference to evaluate their influence on the physical, thermal and mechanical properties of the resulting mortar. According to the results, for both types of fibres studied, the higher the fibre proportion used, the higher were the density, the thermal conductivity, the flexural strength and the compressive strength.of the resulting mortars. Recycled brass fibres increased the thermal conductivity and decreased the volumetric heat capacity of the resulting mortars more than the steel fibres, which is interesting, for example, on self-levelling mortars used on radiant floor heat exchangers. However, less increase was observed on the mechanical properties of the recycled brass fibre reinforced mortars than that of the steel fibre reinforced mortars, due to the shorter length of the former fibres (5-10 mm for the recycled brass fibres, 13 mm for the steel fibres). Therefore, the parameter that controls the cutting frequency of the waste wire of the electrical discharge machine should be modified to adapt the final fibre length to that of the commercially available fibres.

Effect of delayed microwaving on the strength progress of Green alkali activated cement composites

Increasing urbanization around the world has led to the emergence of many problems that must be solved, such as the tendency to use alternative materials for cement to reduce costs and environmental risks. Simultaneously, reducing time and increasing productivity have directed most of the research towards developing the precast concrete industry. In this work, these problems were combined to find an optimal way to solve them by studying the effect of a wide range of microwave radiation on alkali-activated slag (AAS) to increase building quality assurance. The impact of delayed microwave treatment time (1 and 7-days), as well as different wattage scales (0, 90, 450 and 900 W) and treatment period (2, 4 and 8 min) on the mechanical properties of AAS pastes, were examined. The X-ray diffraction (XRD), Thermogravimetric analysis/its derivative (TGA/DTG) and environmental scanning electron microscope (ESEM) were carried out to investigate the composition and morphology of the produced zeolitic phases. The results confirmed that microwave curing is an effective method of increasing the strength for AAS. The low wattage level and the short treatment period are adequate to improve the mechanical properties of AAS at late ages. However, at early ages, curing AAS for 8 min at 900 W increases the strength by 327.2% compared with the control specimen. Delaying the microwave treatment up to 7-days led to an increase in AAS strength up to 34.6% after subjection to 4 min and 900 W.

Application of the C-S-H Phase Nucleating Agents to Improve the Performance of Sustainable Concrete Composites Containing Fly Ash for Use in the Precast Concrete Industry.

Siliceous fly ash (FA) is the main additive to currently produced concretes. The utilization of this industrial waste carries an evident pro-ecological factor. In addition, such actions have a positive effect on the structure and mechanical parameters of mature concrete. Unfortunately, the problem of using FA as a Portland cement replacement is that it significantly reduces the performance of concretes in the early stages of their curing. This limits the possibility of using this type of concrete, e.g., in prefabrication, where it is required to obtain high-strength composites after short periods of curing. In order to minimize these negative effects, this research was undertaken to increase the early strength of concretes with FA through the application of a specifically formulated chemical nano-admixture (NA) in the form of seeds of the C-S-H phase. The NA was used to accelerate the strength growth in concretes. Therefore, this paper presents results of tests of modified concretes both with the addition of FA and with innovative NA. The analyses were carried out based on the results of the macroscopic and microstructural tests in five time periods, i.e., after 4, 8, 12, 24 and 72 h. The results of tests carried out with the use of NA clearly indicate the possibility of using FA in a wide range of management areas in sustainable concrete prefabrication.

The Influence of Steel Fibers on the mechanical properties and thickness of precast concrete panels

Concrete is well-known with its brittleness, low tensile strength and tensile strain capacities. This performance considered as one of the most crucial constraints that facing precast concrete industry. However, it could be improved by the addition of steel fibers which have been used widely in the last few decades. Hence, higher ductility and better arresting ability to crack propagation could be achieved. In Iraq, the precast concrete panels (flags) are commonly used for roofing and usually produced from plain concrete. This study aimed to add small volume fraction of steel fiber to the precast concrete panels to improve the handling and transportation process and assess their breaking load in according to the requirements of the Iraqi standard specification No.1107- 87. Concrete panels with (400×400mm) and different thicknesses (30 and 50mm) were produced. Different steel fiber volume fractions (0%, 0.25%, 0.5%, and 1%) were incorporated. The mechanical properties (compressive strength, splitting tensile strength, and flexural strength) for the concrete mixes were investigated. The test results of this study encourage the incorporation of small volume fraction of steel fiber in production of precast concrete panels to reduce the spoilage upon handling and transportation of precast concrete panels. The breaking load of steel fiber concrete panels has been improved by 142% relative to reference concrete panels. It was also revealed that the concrete panel thickness could be reduced when the steel fiber content increased, which could be of great interest with regards to the economic side. This is because of reducing the amount of raw materials used in production of concrete panels and thereby reducing the impact on the environment. The statistical analysis was accomplished by using the SPSS program.

The effect of combined carbonation and steam curing on the microstructural evolution and mechanical properties of Portland cement concrete

The present study investigated the effect of the combined carbonation and steam curing on the physicochemical properties and CO2 uptake of the Portland cement concrete. Four different curing regimes were adopted during the initial 10 h of curing to evaluate the potential of carbonation curing as an alternative to conventional steam curing in the precast concrete industry from environmental and practical viewpoints. Four combinations of carbonation and steam curing conditions were applied as curing regimes to the samples at an early age. The test results indicated that the samples treated with the combined carbonation and steam curing exhibited higher early strength development compared to the other samples, signifying that carbonation curing can reduce the production time of precast concrete. Furthermore, the CO2 uptake capacity of the samples was calculated and found to be as high as 18% with respect to the mass of the paste samples. Hence, the simultaneous utilization of steam and CO2 for the fabrication of precast concrete members has the potential to make precast concrete greener and more costeffective.

The study of precast pavers production from concrete blocks waste

This work presents part of a study whose main objective is to observe the behavior of the physical and mechanical properties of the materials (raw material) and of products made for the civil construction from the precast concrete industry, such as concrete blocks and pavers for interlocking floors. Through the investigation, was identified the potential of using the concrete blocks waste of the production as aggregates added to the concretes utilized to produce pavers. Thus, it is expected that this work contributes as a basis for obtaining scientific and technical knowledge regarding the materials and procedures that must be adopted for the manufacture of pavers, allowing their production for commercialization.

Resilience

Resilience of concrete structures was the main theme of the fib symposium 2020 in Shanghai, and in this editorial, I present some reflections from my online key-note lecture given at that occasion. I hope that these reflections can offer some food for thought on the future of the construction industry in general and of structural concrete in particular. Resilience stems from the Latin word resilio which means to jump back or to rebound from shocks which occur suddenly or more gradually. In the strict structural sense we can consider resilience of systems related to shock wise events such as explosions, earthquakes, fires, etc. which can be linked to robustness and redundancy. Resilience can also be considered with respect to the capacity of a system or society to resist climate change or pandemics. A further step is to look to the resilience of our society and the industry with respect to digitalization. We cannot deny the huge influence of digitalization on our daily life, characterized by a high degree of interconnectivity and information exchange at an amazingly high speed. The Internet of Things (IoT) is a network of physical objects that are embedded with sensors, software, and other technologies for the purpose of connecting and exchanging data with other devices and systems over the internet. Of course, this IoT also offers some threats and cybersecurity has become a hot topic. Examples of the IoT are smart cities where traditional networks and services are made more efficient with the use of digital and communication technologies to support a city's resilience and sustainability. Artificial Intelligence (AI) has seen a rapid development in recent years, including machine learning and deep learning. In combination with drones appearing on the building sites and with embedded sensors, AI allows an optimized assessment and upgrading approach of existing structures. The implementation in industry of all these new evolutions is often called Industry 4.0, or the fourth industrial revolution. The COVID-19 pandemic has also a disruptive effect on the construction industry in the sense that transformations that were already taking place, will be accelerated. We will evolve to production systems that increasingly make use of modular components, automated manufacturing, robotics supported on-site execution and digital planning and production. All these trends will undoubtedly increase productivity as we experienced in the precast concrete industry. We also see Virtual Reality and Augmented Reality appearing on building sites resulting in a fully interactive 3D experience and thus improving the quality of the built environment. BIM allows to create a virtual model of a building that is made up of dynamic and intelligent virtual building components that contain information about their identity and geometry. The information stored in the BIM model can be extracted from it in various ways: in the form of plans, sections, 3D views, bill of quantities, estimates, space layouts, solar studies, etc. Worldwide we see applications of 3D printing, which allows full flexibility in defining the shape of concrete components and which can even be adapted to an optimized flow of forces, offering additional freedom in conceptual design. In the last decades, concrete evolved from a basic building material towards a tailor-made multi-component cementitious material with varying degrees of alternative binders. A full life cycle analysis results in eco-friendly green buildings within a broader sustainability concept. Without doubt, we live in a challenging era for the construction industry, or are there too many changes in a short time? Important is to look to these changes as an opportunity, to build in a more efficient and smart way: When the wind of change rises, some people build a screen and others a wind turbine. The COVID-19 pandemic also has drawn our attention to the societal impact of engineering. Interdisciplinary engineering approaches will gain more importance and even more important will be the interaction with the social sciences. Last but not least, we should also think about the future of our journal as a valuable source of information for fib members and the concrete world in general. How can we make our journal Structural Concrete resilient towards all new kinds of online solutions, social media networks, knowledge creation and updating from big data, etc.? Let me end these reflections by quoting Darwin: It is not the strongest of the species that survives nor the most intelligent. It is the one most adaptive to change.

CO2 Pretreatment to Aerated Concrete with High-Volume Industry Wastes Enables a Sustainable Precast Concrete Industry

Carbon dioxide (CO2) pretreatment to concrete at the early curing ages is a feasible technique towards achieving a greener and more sustainable concrete industry. However, the carbonation efficienc...

Study on mechanical properties of fiber reinforced self compacting concrete

SCC (Self compacting concrete) is the concrete which can flow in to the entire form work and de-aerated entirely and consolidate by its own self weight. Due to its cohesiveness, it can fill the pores of concrete at any shape and size without bleeding and segregation. This property makes, SCC to use in highly/congested reinforcement presence to pour it on/between the formwork. SCC has been found in Japan, to construct the girders, towers, piers, Liquefied Natural Gas (LNG) tanks, culverts and building structures. In precast concrete industry, the usage of SCC is high where the vibration is not required. This research work concentrates on making SCC with steel fibres for the mix design of M30, M35, M40, M45, M50, M55 and M60. As per the European Federation of National Associations Representing for Concrete (EFNARC) guidelines provided for the SCC, the concrete undergone for its fresh concrete properties tests and satisfied the requirements also the compressive strength, split tensile test and modulus of rupture test on the standard specimens were performed to find its mechanical property with and without fibres. The fiber reinforced self compacting concrete (FR-SCC) has performed well when comparing to the conventional specimen.

Effect of Curing Regimes on the Mechanical and Fresh Properties of Steel Fiber-Reinforced Concrete

Abstract Properties of concrete are affected by its fabrication process such as preparation, mixing, placing, finishing and curing. Since curing process is the ultimate stage of the fresh state of concrete before it is put into service, it is of great significance that is needed to be strictly handled. In the present study, steel fiber reinforced concrete was investigated in terms of different curing regimes including precast technology and comparative analysis was performed. To this end, beams and cubes specimens were fabricated and cured under steam process to represent the applications of precast concrete industry. Findings were compared with the other types of curing regimes. Mechanical behaviors of specimens were evaluated along with their strength development and workability in the presence of steel fiber. Results indicated that adequate workability and mechanical properties were obtained for steam-cured specimens compared to other specimens produced with different curing regimes. However, production parameters such as mixture proportion and fiber dosage were more pronounced for low-strength concrete specimens compared to high strength steam cured concrete specimens.

Development of high-early-strength fiber-reinforced self-compacting concrete

High-early-strength fiber-reinforced self-compacting concrete (FRSCC) is a practical material for the precast concrete industry to double its production capacity. This study developed high-early-strength FRSCC mixtures that achieved a compressive and flexural strength of at least 24 MPa and 3.5 MPa, respectively, at 6 h, using commercially available components, typical mixing procedures, and air curing. A mix design process was developed based on the literature and experimental results. The effect of six different fiber reinforcements on the fresh and mechanical properties of concrete was analyzed. The cost limit was set at 523 USD/m3 to make the concrete mix cost-effective.

Effect of Limestone Powder and Fine Gypsum on the Cracking Tendency of Blast-Furnace Slag Cement Concrete Subjected to Accelerated Curing

Thermal stresses are generated in concrete during the accelerated curing process in precast concrete. These stresses may cause concrete to crack, which would have a negative effect on the general concrete performance. This paper provides the results of the thermal stress analysis of concrete containing 25% replacement of ordinary Portland cement (OPC) by ground granulated blast-furnace slag cement (GGBFS) with 3000 cm2/g fineness. A total of 2.5% of limestone powder and 1.75% of fine gypsum by mass of OPC were incorporated in the other concrete mix proportion to check their effect on the cracking tendency of concrete. The concrete was subjected to heat curing. JCMAC, a 3D finite element analysis software developed in Japan, was used in this study for the thermal stress analysis. The heat curing period of one day, similar to generally used in the precast concrete industry for civil engineering products consisting of 3 h preheating period, heating to a peak temperature of 65 °C and this temperature was kept for 3 h, and lastly cooling was used in the study. A standard precast box culvert model member together with some experimental results obtained in the laboratory were used in the analysis. Lower cracking resistance at 1 day was observed in both mix proportions that would lead to cracking at demolding time. Curing sheets were then introduced in the analysis to cover the precast mold during accelerated curing and this showed improvement in cracking resistance of concrete containing limestone powder and fine gypsum.

Development and Integration of RFID Simulation Based Tool for Improved Schedule Performance in Saudi Arabia Precast Concrete Industry

A construction project is measured as a process that encompasses numerous activities and a huge amount of information of numerous types that are related to each other. Effective project management entails controlling all aspects of a construction project: quality and quantity of work, costs, and schedules to guarantee the accomplishment of the project. The construction industry in the kingdom of Saudi Arabia is implementing off-site construction with precast cement, for its higher quality, short cycle time, and negligible environmental influence. Amongst the various off-site construction approaches, such construction follows a manufacturing method where houses are built in smaller panels in an assembly line. Owing to the complex and exclusive nature of the home building process, prevailing manufacturing concepts such as automated production planning and control system are not applicable to the panelized home production facility. This research aims in the development and integration of radio frequency identification (RFID) technology to for production planning and control system, resulting in improved schedule performance, in Saudi Arabia precast concrete industry. Radio frequency identification is appropriate to numerous construction applications and generates cost savings via increased speed and accuracy of data entry. The study provides a set of helpful protocols for the deployment of passive RFIDs for automated on factory management of precast concrete operations. Further it aims at paving the way for managing the site for the sake of attaining the desired goals considering the guarantee of achieving high quality and quick conveyance to the related sites which, hence, prompts auspicious conveyance of development ventures. The study is beneficial for the construction professionals to assess the prevailing construction quality perception and the expectations from implementation of any quality improvement technique in construction projects.

Reducing energy consumption of prefabricated building elements and lowering the environmental impact of concrete

In this study, we attempt to improve the energy efficiency in the precast concrete industry by eliminating thermal treatment and reducing the environmental impact of concrete by using ground granulated blast furnace slag (GGBS) and ultrafine Portland cement (UC). We studied several substitute materials such as UC and GGBS with ultrafine and standard particle fineness values. Thermal treatment is used in the prefabrication industry to achieve concrete with high strength at an early age (~13 h) and allow continuous production. UC was added to study the possibility of eliminating steaming by replacing it with an exothermic reaction generated by the UC. GGBS was used as a partial substitute for cement to reduce the carbon dioxide emission footprint produced by the cement industry.The compressive strength following the addition of UC was encouraging. A 90% evolution at an early age was observed for concrete samples with 42% UC and 42% GGBS with heat treatment. In addition, when using the same composition, a 66% increase was observed without heat treatment. The use of GGBS or fine particles improved the carbon footprint without compromising the compressive behaviour of the concrete.