Concrete floors are widely used in industrial areas, both indoors and outdoors. For example, warehouses or industrial processing areas in general, and external storage areas or goods handling, but also for the construction of transit routes such as airport runways and, especially abroad, of road routes for wheel traffic (Bado et al., 2021). In recent years the technological evolution in industrial environments and logistics has increasingly heightened the importance of similar concepts in flooring owing to heightening revolutions in regulatory requirements. Concrete floors are often made solely based on assumptions without any preliminary designs. The result of the lack of planning attention has often led to defects such as cracks, deformations, breaks, and unevenness that compromise the functionality of the flooring (Mapa et al., 2020). From a structural point of view, the floors are plates on continuous and yielding support.
The design of concrete floors is of great importance and topicality. Despite the necessity of such considerations, this sector has often been considered as one that is characterized by engineering incompetence. This is patently in contrast with the numerous technical aspects involved, starting from the characteristics of the support, continuity of the concrete technology, and finally, the surface finishes layer. As such, required checks must be carried out above all against the Exercise Limit State (ELS) (Wu et al., 2017). According to Porras et al. (2020), such considerations should not neglect operation conditions that particularly indicate the limit state of crack formation and the deformation states. These are critical as excessive deformation could create problems. Such problems constitute shelving, the transit of vehicles, and, in general, the functionality of the flooring itself. Flooring can be made by adopting different construction techniques. These comprise non-reinforced concrete flooring, reinforced concrete pavements, flooring in fiber-reinforced concrete (FRC) with conventional reinforcement, and FRC flooring without conventional reinforcement (Mateos et al., 2019).
Depending on the construction techniques adopted, the reinforcement of a pavement consists of one or several layers of net and/or “structural” fibers. According to Mateos et al. (2020), other types of “non-structural” fibers can serve as additions to counteract shrinkage cracking. In the presence of seismic loads, such as those transmitted by pallet racking or similar, fixed to the floor with dowels of the type mechanical or chemical, the pallet transmission cannot be adopted but must be used as a flooring mechanism with conventional reinforcement. In such cases, the designer will be required to verify the need to arrange the reinforcement both on the intrados and on the extrados (Loganathan & Souliman, 2017). Alternatively, the designer can deploy FRC flooring, with or without integrative traditional reinforcement.
The design alternatives related to concrete pavements involve rather complex states. For example, moving loads cause variable cyclical actions, so the flooring is subjected to bending actions with tensile stresses both at the intrados and on the extrados of the plate (Wu et al., 2017). When the tensile stresses exceed the tensile strength of the concrete (under operating conditions), a careful evaluation of the phenomena is necessary for relation to cracking and the use of traditional reinforcement and/or the use of FRC. The design of a concrete pavement consists of two distinct operations. According to Mapa et al. (2020), these comprise the calculation of the thickness of the slab (based on the characteristics of ground lift, the flexural strength of the concrete, the nature and extent of the stresses to which the flooring is subject), and the sizing of the joints. Further, Mapa et al. (2020) indicated that the joints are made in the paving slab to accommodate the deformations and the dimensional variations with respect to the ground and other structural elements, ensuring the at the same time a correct transmission of stresses.
There are three types of joints commonly used in concrete floors. According to Porras et al. (2020), these include contraction or control joints, insulation or expansion joints, and construction joints. The contraction joints and the insulation joints are made to allow movement differentials that are generated in the floor due to the volume variations based on plastic, hygrometric, or temperature variations shrinkage. Indeed, if the deformations are prevented by the presence of constraints, traction stress is established that can exceed the resistance developed up to that moment by the concrete. With the same deformation the effort induced meaning that (σ = Εε) is greater than the elastic modulus (Bado et al., 2021). It follows that the stress that is generated during plastic shrinkage is always less than that due to shrinkage hygrometric, with the same deformation. In floors made of ordinary concrete (i.e. not with compensated shrinkage), it is not possible to prevent the appearance of cracks, but just check both the formation and the amplitude so that the solution of continuity generated does not cause problems of a functional nature (Wu et al., 2017).
The goal of this study is to understand the already known influence of the relative humidity in the CTE of HESC to later understand the effect in the strains of the concrete. This strain, along with shrinkage and load-induced strains produce tensile stresses that could exceed concrete strength, and not having a failure in this situation is something that is also part of the scope of this project. It is important to understand the role played by tensile creep and microcracking to reduce stresses. This study is not only focused on the understanding of the mechanisms but also on the contribution of tests and methods that could appropriately capture the effect of these behaviors. The final part of the study consists of providing some guidance in how to account for and/or include the new approaches into design methodologies. It is important to remark that it is outside the scope to develop design methods or failure models.
The objectives of this study stem from the identification of several gaps in the literature. For instance, the research on bonded concrete overlays using early-high strength concrete mixes not only have produced good results and overall, very good performance but along with that, it was found that some mechanisms and results are either not clear and difficult to understand or there is no available knowledge let alone a validated model to explain them. Three literature gaps have been identified preceding the review of current literature. (1) there is a lack of understanding of the influence of the relative humidity on the coefficient of thermal expansion. It is agreed that the effect is real but both, the mechanism and the corresponding prediction model are big unknowns that need to be solved. (2) Literature owes not provide ample information to help understand tensile creep under different humidity conditions, as a stress-release mechanism of very high stresses on EHSC mixes in the pavement. Currently, there are no tests that could capture tensile creep in the laboratory and field, nor models that could predict tensile creep accurately. (3) The extent of microcracking as a stress-release mechanism for shrinkage and loading stresses is understudied. There is a general agreement on the existence of this phenomenon and its main factors but there are no clear approaches of how to measure, predict and apply this mechanism into design analysis. Addressing this gap will contribute to advancing knowledge in the topic by providing empirically based information concerning the effects of high early strength concrete thermal contraction, shrinkage, and creep on pavement performance.
To write the literature review, the following online databases and search engines were used: Google Scholar, Educational Resource Information Center (ERIC), Ingenta Connect, JSTOR: Journal Storage, ProQuest Criminal Justice, PsycInfo, EBSCO, PsycARTICLES, and Journal Seek. The key search terms and combination of search terms that were input to various online databases included the following: Concrete pavements, thermal contraction, tensile creep, shrinkage, CTE, relative humidity, micro-cracking, EHSC mixes, hygrothermal stresses, structural response, pavement design, and Pavement Management System. All the key terms used were able to yield studies that were relevant to the problem and research questions. Using these keywords (both individually and in combinations), relevant studies were generated from database searches. Only those deemed to be relevant to the current study were included in the literature review. In this literature review, the researcher will expand on the background of the study as provided in the earlier chapter. The first section will identify the search strategy used to acquire literature for writing the literature review. The second section will focus on the theoretical framework for the study, which is the Pavement Condition Index Model (PCI).
Theoretical Framework
The Pavement Management Systems Framework (PMS)
It will be essential to foster the acquisition of insights into the already established influences of strains such as relative humidity, shrinkage, and load in generating tensile stresses that often exceed concrete strength to help develop more effective and sustainable concrete pavement management mechanisms. The Pavement Management Systems (PMS) framework that was developed by the American Association of State Highway and Transportation provides the appropriate foundation for a study with such intentions. According to Di Mascio and Moretti (2019), the PMS framework emerged from considerations into the necessity of concrete pavement design and maintenance based on the need to deploy simple procedures and experiential knowledge to design and assess pavement functionalities. The PMS framework holds that the assessment and management of concrete pavements should be based on knowledgeable insights into factors affecting pavement performance such as thermal and shrinkage elements. Thus, the model suggests the use of coordinated information-based activities for the provision of actionable oversight in matters related to pavement planning, pavement design, maintenance, and evaluation.
Justification for the use of the PMS model in this study stems from its ability to help understand the functionality components encompassed in concrete pavements. Commenting on the usefulness of the framework in studies related to concrete pavement, Khavandi Khiavi and Mohammadi (2018) posited that PMS ensures that engineers understand the influences generated by components such as thermal contractions, creep, and shrinkage in relation to the sustained effectiveness of concrete pavements by generating insights from databases containing pavement information and the use of analysis schemes that provide critical information concerning possible optimization measures. Further, the model is essential for the current study because it helps determine the impacts of shrinkage, creeping, and thermal contractions based on schematic analysis of data using computerized approaches that promote the acquisition of information to foster performance prediction (Saha et al., 2017).
The PMS model has been used in previous studies that are related to the topic under study. For instance, de Moura et al. (2018) investigated the evaluation of pavements in airports seeking to generate maintenance strategies. Using a systematic literature review approach, the researchers studied components such s thermal contraction, creeping, and shrinkage in relation to the sustained efficiency of airport pavements. The researchers also explored these components connecting each to the PMS model to determine appropriate design and maintenance decisions that could suit the need to improve the strength of pavements through treatment and rehabilitation. Drawing information from databases like Web of Science and Scopus, the researchers acquired and used 283 previous studies that were related to pavement strength and maintenance. de Moura et al. (2018) found out that sufficient prediction of pavement conditions could be attained by considering the impacts exerted by thermal contractions, creeping, and shrinking on pavement strength and efficiency.
References
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de Moura, I. R., dos Santos Silva, F. J., Costa, L. H. G., Neto, E. D., & Viana, H. R. G. (2020). Airport pavement evaluation systems for maintenance strategies development: a systematic literature review. International Journal of Pavement Research and Technology, 1-12. https://doi.org/10.1007/s42947-020-0255-1
Di Mascio, P., & Moretti, L. (2019). Implementation of a pavement management system for maintenance and rehabilitation of airport surfaces. Case Studies in Construction Materials, 11, e00251. https://doi.org/10.1016/j.cscm.2019.e00251
Khavandi Khiavi, A., & Mohammadi, H. (2018). Multiobjective optimization in pavement management system using NSGA-II method. Journal of Transportation Engineering, Part B: Pavements, 144(2), 04018016. https://doi.org/10.1061/JPEODX.0000041
Loganathan, K., & Souliman, M. (2017). Prediction of average annual surface temperature for both flexible and rigid pavements. Journal of Materials and Engineering Structures «JMES», 4(4), 259-267. http://hdl.handle.net/10950/2342
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Mateos, A., Harvey, J., Bolander, J., Wu, R., Paniagua, J., & Paniagua, F. (2019). Field evaluation of the impact of environmental conditions on concrete moisture-related shrinkage and coefficient of thermal expansion. Construction and Building Materials, 225, 348-357. https://doi.org/10.1016/j.conbuildmat.2019.07.131
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