Precast Concrete Units Research Articles

Displacement analysis of a geogrid-reinforced retaining wall with modular precast concrete facing

Reinforced earth retaining walls are widely used in transportation projects, such as embankments, bridge access roads, and bridge abutments. When the wall height is large, the weight of the embankment soil and vehicle loads can cause large wall displacements, thereby affecting the serviceability of the wall system. Although many retaining wall projects use wall-facing structures assembled from precast concrete components, most domestic studies have focused on continuous reinforced concrete wall-facing structures. Therefore, to understand the displacement behavior of reinforced retaining walls when the wall height is large, we investigated the displacement behavior of an earth retaining wall in the My Phuoc-Tan Van overpass project, Binh Duong Province. This study uses a finite element simulation that considers the nonlinear behavior of backfill soil, foundation soil, geotextiles, and the interaction between precast concrete units.

Test, modelling and design of a demountable stainless steel bar connection system for precast concrete pavements

To promote the reuse of precast concrete pavement units, an innovative demountable stainless steel bar connection system is proposed in this paper. Monotonic load tests were conducted to investigate the effects of the width of the stainless steel bar connection, the width and the end distance of the stainless steel plate on the mechanical behaviour of the proposed connection system. As localised concrete crushing was observed after tests, the stainless steel bar connection system was updated with an expanded contact area between concrete and steel. Test results revealed that specimens with the updated connection system exhibited high initial stiffness with low concrete compressive stress concentration. Finite element analysis (FEA) was then carried out to further investigate the parameters that affected the structural performance of the updated connection system. According to the deformations of the stainless steel bar connection and high-strength bolts, an analytical approach was developed to predict the design load of the proposed connection system. Design recommendations were finally summarised based on the obtained test and parametric analysis results to guide the demountable connection design.

Estimation of Flexural Strength of Plain Concrete from Ultrasonic Pulse Velocity

The aim of this study is to propose mathematical expressions for estimation of the flexural strength of plain concrete members from ultrasonic pulse velocity (UPV) measurements. More than two hundredpieces of precast concrete kerb units were subjected to a scheduled test program. The tests were divided into two categories; non-destructive ultrasonic and bending or rupture tests. For each precast unit, direct and indirect (surface) ultrasonic pulses were subjected to the concrete media to measure their travel velocities. The results of the tests were mointered in two graphs so that two mathematical relationships can be drawn. Direct pulse velocity versus the flexural strength was given in the first relationship while the second equation describes the flexural strength as a function of indirect (surface) pulse velocity. The application of these equations may be extended to cover the assessment of flexural strength of constructed concrete kerb units or in-situ concreting kerbstone and any other precast concrete units. Finally, a relation between direct and indirect pulse velocities of the a given concrete was predicted and suggested to be employed in case when one of the velocities is notavailable can be measured for other ultrasonic pulse test applications

Reuse of Powders and Recycled Aggregates from Mixed Construction and Demolition Waste in Alkali-Activated Materials and Precast Concrete Units

This article describes the recycling of coarse and fine fractions and powder from construction and demolition waste (CDW) using alkaline activation technology (geopolymerization). The CDW sample used corresponds to a mixture (mixed waste) of concrete (Co), ceramics (Ce) and masonry (M). Co, Ce and M (CDW-Mixed) powders were used as geopolymer precursors. As an alkaline activator, a mixture of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used. From CDW-Mixed, a hybrid cement added with 10% ordinary Portland cement (OPC) was synthesized to promote curing at room temperature (25 °C). From the alkali-activated hybrid cement and the incorporation of mixed recycled aggregates (gravel and sand), applications of mortars, concretes, fiber-reinforced materials and prefabricated units, such as solid blocks, perforated (hollow) blocks and pavers, were produced. The results of the physical–mechanical characterization validate the application potential of these CDW-based materials in the construction sector. Compressive strengths of up to 40.5 MPa for mortar and 36.9 MPa for concrete were obtained after 90 days of curing at room temperature ≈ 25 °C. Similarly, a life cycle analysis (LCA) associated with raw materials demonstrated the environmental sustainability (44% lower carbon footprint) of mixed alkali-activated CDWs compared to conventional materials based on OPC.

FIELD DATA ANALYSIS OF HOME-BASED STORMWATER ON-SITE DETENTION SYSTEM

This paper describes the field test of a stormwater detention system which is a system designed to hold a specific volume of water and release it slowly over time, in this test case precast concrete modular units are assembled in a residential car porch and connected to a partial roof catchment via a downpipe. Stormwater is held and stored temporarily within the chambers created by the precast concrete pieces. Rainfall and flow data associated with the detention system in terms of the inflow, outflow and water levels data are collected and verification process are performed by comparing the collected data to design data for the intended system. Analyses of five storm events confirm that the estimated design inflow, outflow and water levels in response to 5- and 10-minute 10-year Average Recurrent Intervals (ARI) design rainfall are safe against the actual rainfall and actual detention and discharge performances.

The use of balanced lowering method technology for bridge construction in cramped urban environments

The main trends in bridge building are: the implementation of new materials, the assimilation of novel technologies, and the construction time reduction. The new technologies assimilation is often associated with the need to build bridge structures in cramped conditions. Considered by the author balanced lowering method technology corresponds to these trends. The technology was developed at the Vienna Technical University, the main idea is to assemble the supporting elements in a vertical position with subsequent deployment to the design horizontal position. To reduce the weight of the mounted elements, this technology uses thin-walled prestressed precast concrete units. After installing it in the design position, they perform the function of leave-in-place form and are cast in place directly on the construction site. This technology was invented for high pier bridges to eliminate the erection and dismantling of temporary support but has recently been shown to be cost-effective for low pier bridges. The advantage of this method is not only the construction time reduction and the free underbridge clearance presence but also the fact that the braces are not only a mechanism for turning the span into a horizontal position but also allow to reduce the estimated span length. The article discusses the bridge projects across the Lafnitz and Lahnbach rivers in Austria, as well as previous options for bridge projects. Particular emphasis in the work is placed on the bridge construction technology consideration, the main technological stages identification, as well as the performance features of certain works. The author presents recommendations on the application of this construction method.

Flexural mechanism and design method of novel precast concrete slabs with crossed bent-up rebar

Precast concrete slabs are one of the most widely used types of structural member in building industrialization. In this paper, a novel precast concrete slab with crossed bent-up rebar was proposed, where the rebar of precast concrete units was bent-up and embedded crossways in cast-in-place concrete toppings, forming a novel joint configuration of precast concrete slabs. The effects of two bent-up angles of the rebar in the precast concrete units, different thicknesses of the cast-in-place concrete toppings, and different reinforcement ratios on the failure modes of novel precast concrete slabs were studied using flexural loading tests with eight specimens. The failure modes of the specimens changed from the joint failure to the failure of the termination section of lap-splice rebar (TSLSR), when the horizontal angle of the bent-up rebar changed from 90 to 60°. Bent-up ends with an angle of 60° prevented the joint failure of the novel precast concrete slabs, and strengthened the flexural performance of the joint. The horizontal component force of the bent-up ends markedly strengthened the flexural capacity of the joint, and the vertical component force of the bent-up ends made the precast concrete units connect tightly with the cast-in-place concrete toppings, enhancing the anchorage effectiveness of the lap-splice rebar. There were two primary failure modes of the specimens: joint cracking caused by the yield of the lap-splice rebar in the joint, and plastic cracking failure of the section beyond the TSLSR. Finally, the design equations of the flexural capacity of the joint and the anchorage length of the bent-up ends were established, and the design process of the novel precast concrete slabs was given.

Pilot Scale Production of Precast Concrete Elements with Wood Biomass Ash.

Downsizing fossil fuel dependence and greenhouse gas emissions is at the forefront of a sustainable future. The expansion of renewable energy while striving to minimize dependence on fossil fuels has led to biomass taking the lead among renewable energy sources, with wood having the broadest application. Along with the growing trend of using biomass as a renewable energy source, the combustion of wood biomass results in wood biomass ash (WBA), leading to compelling amounts of waste. In this study, the technical feasibility of fly WBA from different Croatian power plants was analyzed to evaluate its potential use in precast concrete drainage elements and curb units. By implementing a performance-based design, the influence of various factors in thermal processing of wood biomass was investigated, together with a detailed characterization of WBA in order to assess the feasibility of using WBA as a secondary raw material in a large-scale industrial batching plant. The compressive strength and durability properties (water absorption, permeability, and freeze–thaw resistance) of concrete mixtures with WBA as a replacement for 15 wt% cement were evaluated and compared with the precast concrete manufacturer’s technical requirements. The main concerns identified were compositional inconsistency of WBA, workability downturn, delay in initial reactivity rate, and increased water absorption. Concrete with WBA based on a circular design has been found to be a viable solution to cement depletion, stepping up from recycling to reuse of industrial waste.

Developing a system for assessing the sustainability in school building projects

In recent times, the concept of sustainability has become a focus of attention for many institutions and communities. The reason for the spread of this concept and great interest is the pursuit of sustainable development of societies which aims at balancing the three factors: environmental, economic, and social. This paper aims to develop a system to implement sustainability ideas in school building projects based on the international guidelines and practices for sustainability. For example, (Building Research Establishment Environmental Assessment Method (BREEAM)-Leadership in Energy and Environmental Design (LEED)-The Pearl Building Rating System (PBRS)) and the current practices in Iraq. The purpose of the collected and reported information was for making decisions during various stages of preconstruction, construction, and post-construction. The system employed suitable criteria, subcriteria, and standard weights for school buildings assessment, which was set according to a field survey. The survey included interviewing a group of specialists in school buildings and conducting a closed questionnaire. A computer program was prepared to assess school buildings in the 3rd General Directorate of Education in Baghdad-Karkh. These buildings were executed during (2008–2018). The School buildings were classified into four types (traditional, precast concrete units, steel structures, and structural concrete construction). The field survey has shown that the highest standard of sustainability is the environmental design (20.79), and the lowest sustainability criteria are water treatment system (5.81). However, the study aims to develop a sustainability assessment system for school buildings. A comparison was made between the current buildings with ones that having ideal sustainability criteria. Similarly, a monitoring was done with the perfect situation to observe the deviation within the project progress. Finally, recommendations were given for the purpose of employing the sustainability concepts in school buildings.

EVALUATING THE EFFICIENCY OF HOUSEHOLD STORMWATER DETENTION SYSTEM

This paper describes the evaluation of water storing capacity of a household stormwater detention system based on field data. Collection of field data is often sidelined due to the cost and human capital incurred. However, the true value of field data is demonstrated here by comparing the observed and design data. A field test is completed in a real-life terrace house, utilizing the house’s 95m2 side canopy as roof catchment and 4.40m x 4.70m car porch area to station a detention tank. Precast concrete modular units with 3.9m3 effective storage volume are assembled within the tank. Downpipe with 0.1m diameter is installed to connect the roof gutter to the detention tank; while pipeline with 0.05m diameter is installed as the outlet from tank to the house perimeter drain. The mentioned setup is subjected to actual rainfalls from December 2019 till February 2020 that corresponded with the peak of Northeast Monsoon season. Ten observed storm events with peak hourly total rainfall readings ranging from 22 to 48mm are selected for analysis. Rainfall and water level readings from the field test allow the derivation of roof runoff volume and detained water volume in the tank. It is found that the household stormwater detention system is able to capture about 50% of the roof runoff. However, the current setup is found to cause flooding for rainfall over 40mm. The flooding issue, however, is undetected by the design data that underestimated the water storing capacity. This is due to the use of uncommon precast concrete modular units that may not have its flow characteristics represented by existing formula and model. No matter how uncommon the modular units be, various types and forms of stormwater detention system are becoming the new normal in the industry and field test is the best tool to validate their performances.

Masonry mortars, precast concrete and masonry units using coal bottom ash as a partial replacement for conventional aggregates

Granular coal combustion products are problematic waste materials whose use as aggregates in concrete has been extensively studied. However, its integration into other non-structural materials and elements has not been so widely documented. Masonry mortars, precast concrete and masonry units with different ratios of coal bottom ash replacing conventional aggregates have been studied. With the incorporation of coal bottom ash in the mortars, the workability, density and strength decrease whereas the porosity, the weight loss and the drying shrinkage increase. However, low replacement ratios have slight effects. The use of coal bottom ash as an internal curing water reservoir is proposed as the most promising future line of research.

Erratum to: “The truth about the geopolymers” S. Grzeszczyk, Cement Wapno Beton, 26(3) (2021), 101 – 108

In my article “The truth about geopolymers” by S. Grzeszczyk, Cement Wapno Beton, 26 (3) (2021), 101-108, there is an information I would like to rectify. There is a sentence: “Industrial application of geopolymers in Poland is limited to the activity of professor Maolepszy, who used this binder of blast furnace slag activated with NaOH addition to the construction of the students’ hotel, in Cracow.” It should be: “The activity of professor Małolepszy includes the use of a slag-alkali binder, in which the activator was sodium carbonate. This material was used for the manufacturing of precast concrete units of the” Żerań “type, of which a building was erected in the 1970s in the area of the “Prefabet” company in Kraków, Poland. This building was examined for twenty years in terms of concrete strength and durability. In practice, a total of about 100 thousand cubic meters of slag-alkali concrete has been used in Poland.”

HOMOGENEOUS LOW-CRESTED STRUCTURES FOR BEACH PROTECTION IN CORAL REEF AREAS

In many countries, the health of the marine ecosystems and the sun-sand-sea tourism depend on the coral reefs, which have been retreating around the world during the last decades. Homogeneous Low-Crested Structures (HLCS), made of large rocks or pre-cast concrete units, can be placed to mimic the functions of beach protection and eventually serve as a refuge for species. HLCS is a type of multi-purpose green infrastructure which is functionally similar to conventional low-crested structures but have higher porosity and are more easily dismantled for re-use. Contrary to conventional low-crested structures, the functionality of HLCS protecting beaches depends on the selected placement grid; this paper describes physical and numerical placement tests on horizontal bottom used to characterize the layers coefficients of Cubipod HLCS. The Bullet Physic Engine (BPE) numerical model used in the gaming industry, which is based on the rigid body method, is calibrated using the physical placement tests. The layer coefficients of Cubipod HLCS measured in the physical placement tests were similar to those obtained with the BPE numerical model, which could be used to optimize placement grids of HLCS on specific sea bottom conditions. Finally, the influence of the placement grid of Cubipod HLCS on the structure height, crest freeboard and wave transmission is analyzed.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5bi-jpuJYcQ

Crack and deformation behavior of composite beams using partial‐depth precast concrete units

AbstractIn ranges with negative moments, crack formation influences the structural behavior of statically indeterminate composite beams under service conditions. Composite beams with partial‐depth precast concrete units show some particularities, which cannot be described accurately using the established methods of calculation. This article presents methods of calculation, which can be used to cover the specific structural behavior and describe crack formation, crack widths and deformations realistically.

Flexural and Shear Performance of Prestressed Composite Slabs with Inverted Multi-Ribs

Half precast concrete slabs with inverted multi-ribs (Joint Advanced Slab, JAS), which enhance composite performance between slabs by introducing shear keys at connections between the slabs and improve structural performance by placing prestressing tendons and truss-type shear reinforcements, have recently been developed and applied in many construction fields. In this study, flexural and shear tests were performed to verify the structural performance of JAS members. Towards this end, two flexural specimens and four shear specimens were fabricated, and the presence of cast-in-place concrete and the location of the critical section were set as the main test variables. In addition, the flexural and shear performance of the JAS was quantitatively evaluated using a non-linear flexural analysis model and current structural design codes. Evaluation results confirmed that the flexural behavior of the JAS was almost similar to the behavior simulated through the non-linear flexural analysis model, and the shear performance of the JAS can also be estimated appropriately by using the shear strength equations presented in the current design codes. For the JAS with cast-in-place concrete, however, the shear strength estimation results differed significantly depending on the way that the shear contributions of the precast concrete unit and cast-in-place concrete were calculated. Based on the analysis results, this study proposed a design method that can reasonably estimate the shear strength of the composite JAS.

Research of the industrial facility underground structures settlement caused by its machinery dynamic loads

The article is devoted to the issue of research of the soil basement vibrocreep negative impact, which takes place underdynamic loads. The results of on-site measurements of industrial facility underground structures forced dynamic vibrationsparameters have been presented. The influence of the dynamic vibrations value on the development of underground cablechannel precast concrete units uneven settlement has been analyzed. The interrelation between the value of the channel builtupconstruction settlement at the point of measurement and the amplitude of forced vibrations at this point has been determined.

Finite difference time domain modelling as support to ground penetrating radar surveys of precast concrete units

ABSTRACTPrecast concrete elements are commonly employed in the construction industry, however failing to comply with manufacturers’ guidelines and poor construction practice can lead to loss of efficiency compromising the usability of the building. This paper presents two case studies where ground penetrating radar surveys, performed to investigate the cause of failure of precast concrete elements, were supported by the finite difference time domain numerical approach. In the first case, the model was built after the survey for a better understanding of the complex reflection patterns unexpectedly experienced and to provide a clear interpretation; in the second case, the numerical simulation was performed prior to the survey, according to the information already available on the precast unit. The synthetic radargrams were then used as a valuable reference to assess the precast element internal conditions: on site, the comparison of the real radargrams with the synthetic ones allowed to address safely the intrusive works necessary to determine the concrete quality and during the processing step, any deviation from the ideal ground penetrating radar response gave potentially an indication of anomalies in the assembly operations that could be identified. The finite difference time domain method should then be considered as complementary to ground penetrating radar surveys aimed to investigate precast elements.

Experimental Study on an Optimized-Section Precast Slab with Structural Aesthetics

The optimized-section precast slab with structural aesthetics (OPS) is a half precast concrete slab with multi-ribs that optimizes the cross-section by eliminating the unnecessary bottom flanges at mid-span and has good structural performance by utilizing prestressing strands and truss-type shear reinforcements. In addition, it is a member that is designed to highlight the structural aesthetics through the curved shape of a variable cross-section at the bottom of the flange which is created from a natural shape that is formed in the section optimization process. In this study, experimental research was carried out to examine the structural performance of the OPS, which includes flexure and shear tests on the precast concrete unit members for resisting construction loads, the composite members with cast-in-place concrete, and the continuous end section. The experiment results confirm that, in accordance with the current design code, the flexural performance of OPS is on the safe side regardless of the member type, whereas the shear performance of the precast concrete unit member differs slightly from that of the composite member due to the differences in the contributions of the shear reinforcement as the effective depth varies.

Accelerated carbonation curing of cement mortars containing cement kiln dust: An effective way of CO2 sequestration and carbon footprint reduction

Accelerated Carbonation curing (ACC) is an innovative curing procedure for precast concrete units, which results in sequestration of the carbon dioxide gas and its conversion into stable products. The effect of carbonation curing on mortar mixes incorporating cement kiln dust (CKD) as partial replacement of cement has been investigated in the present study. Carbonation curing was carried out for 12 h, followed by either sealed bag curing or water spray curing for 3 days. The effect of carbonation curing was studied in terms of compressive strength, porosity and pH of the mix, along with SEM to study the resultant morphology. It was observed that ACC led to better early age strength and lower porosity as compared to water cured mortars with at least 20% increase in the strength for each mix. The later age strength decreased slightly by ACC due to water loss, but could be compensated by adopting subsequent water spray. The microstructure analysis showed presence of C-S-H gel and CaCO3 for the carbonated mortars, contributing to the additional strength and reduced porosity. Stoichiometric analysis of the control mix at 3 days of casting also confirmed that carbonation curing enhances the compressive strength and decreases porosity of the mix. It was observed that the finer particle size of CKD particles and presence of alkali in CKD further promotes the carbonation reaction, and hence led to large improvement in the properties of the resultant mix.

Influence of Concrete Mix Transportation with Inertia Conveyor on Concrete Properties

The practical expediency of the study of physical and mechanical properties of concrete, received from the mix, exposed at its feeding to the point of placement to the transportation with the inertia conveyor by means of original technology, which shows its competitiveness at factories producing precast concrete units, is proved. The experimental procedures of the research performed by the authors, where they analyzed the process of transportation relating to the use of ready-mix concrete on the dense aggregate, are described. The data on the effect of received previously rational values of the major parameters of engineering process studied (the parameters of asymmetric oscillations of work member of the conveyor and the thickness of the mix layer moved by it) both on the homogeneity of fresh concrete and the strength and strength homogeneity of hardened concrete are represented and analyzed.