Experiment and Analysis of Mechanical Properties of Lightweight Concrete Prefabricated Building Structure Beams

Recent years have witnessed that the prefabricated concrete structure is in the widespread use of building structures. This structure, however, still has some weaknesses, such as excessive weight of components, high requirements for construction equipment, difficult alignment of nodes, and poor installation accuracy. In order to handle the problems mentioned above, the prefabricated component made of lightweight concrete is adopted. At the same time, this prefabricated component is beneficial to reducing the load of the building structure itself and improving the safety and economy of the building structure. Nevertheless, it is rarely found that the researches and applications of lightweight concrete for stressed members are conducted. In this context, this paper replaces ordinary coarse aggregate with lightweight ceramsite or foam based on the C60 concrete mix ratio so as to obtain a mix ratio of C40 lightweight concrete that meets the engineering standards. Besides, ceramsite concrete beams and foamed concrete beams are fabricated. Moreover, through three-point bending tests, this paper further explores the mechanical properties of lightweight concrete beams and plain concrete beams during normal use conditions. As demonstrated in the results, the mechanical properties of the foamed concrete beam are similar to those of the plain concrete beam. Compared to plain concrete beams, the density of foamed concrete beams was lower by 23.4%; moreover, the ductility and toughness of foamed concrete were higher by 13% and 3%, respectively. However, in comparison with the plain concrete beam, the mechanical properties of the ceramsite concrete beam have some differences, with relatively large dispersion and obvious brittle failure characteristics. Moreover, in consideration of the nonlinear deformation characteristics of reinforced concrete beams, the theoretical calculation value of beam deflection was given in this paper based on the assumption of flat section and the principle of virtual work. The theoretically calculated deflection values of ordinary concrete beams and foamed concrete beams are in good agreement with the experimental values under normal use conditions, verifying the rationality and effectiveness of the calculation method. The research results of this paper can be taken as a reference for similar engineering designs.

Mechanical Properties and Fracture Energy of Concrete Beams Reinforced with Basalt Fibres

Fibre-reinforced concrete (FRC) is widely employed in the construction industry, with assorted fibre types being used for different applications. Typically, steel fibres give additional tensile strength to the mixture, while flexible fibres may be used in large sections, such as floor slabs, to control crack width and to improve the handling ability of precast sections. For many reasons, including durability concerns, environmental impact, thermal performance, etc, alternatives to the currently available fibres are being sought. This study examines the potential of using basalt fibres, a mineral and natural material, as reinforcement of concrete sections in comparison to steel fibres and plain concrete mix. Mixes were tested containing 0.5% and 1.0% of basalt fibres measuring 25mm length, 0.5% of the same material with 48mm length and steel fibres measuring 50mm by 0.05%, 0.1%, 0.15% and 0.2% of the concrete volume. For the mechanical performance analysis, the 3-point bending test was led and the fracture energy, Young’s modulus and tensile strength in different moments of the tests were calculated. When compared to the control mixtures and the steel-fibre-reinforced concrete, the mixes containing basalt had a reduction in their elastic modulus, representing a decrease in the concrete brittleness. At the same time, the fracture energy of the mixtures was significantly increased with the basalt fibres in both lengths. Finally, the flexural strength was also higher for the natural fibre reinforced concrete than for the plain concrete and comparable to the results obtained with the addition of steel fibres by 0.15%.

New Long-Life Concrete Pavements in the Czech Republic

A jointed plain concrete pavement represents a reliable, historically proven technical solution for highly loaded roads, highways, airports and other industrial surfaces. Excellent resistance to permanent deformations (rutting) and also durability and maintenance costs play key roles in assessing the economic benefits, rehabilitation plans, traffic closures, consumption and recycling of materials. In the history of concrete pavement construction, slow-to-normal hardening Portland cement was used in Czechoslovakia during the 1970s-1980s. The pavements are being replaced after 40-50 years of service, mostly due to vertical slab displacements due to missing dowel bars. However, pavements built after 1996 used rapid hardening cements, resulting in long-term surface cracking and decreased durability. In order to build durable concrete pavements, slower hardening slag-blended binders were designed and tested in the restrained ring shrinkage test and in isothermal calorimetry. Corresponding concretes were tested mainly for the compressive/tensile strength evolution and deicing salt-frost scaling to meet current specifications. The pilot project was executed on a 14 km highway, where a unique temperature-strain monitoring system was installed to provide long-term data from the concrete pavement. A thermo-mechanical coupled model served for data validation, showing a beneficial role of slower hydration kinetics. Continuous monitoring interim results at 24 months have revealed small curling induced by drying and the overall small differential shrinkage of the slab.

Long-Term Performance of Jointed Plain Concrete Pavement with Rapid Strength Concrete On California Highways

Rapid Strength Concrete (RSC) slabs on six California jointed plain concrete pavement (JPCP) highway projects were surveyed. These projects had been previously surveyed in 2008 at 3-years of age and by 2018 had reached a service life of 13-years. Of the initial 5430 slabs examined in 2008, a total of 1493 RSC slabs, located on 12 traffic lanes, were observed and distress types recorded again in 2018. These slabs included both CTS and 4x4 RSC located in both inner and outer lanes. Only a small percentage (1.4%) of the 5,430 RSC slabs exhibited any distress in 2008 after 3-years' service and the increases were small over the next 10 years of service with the exception of transverse fatigue cracks. The transverse (top down fatigue) type of cracking had the highest percentage and largest increase of any distress type. The heavy truck outside lanes exhibited 21% transversely cracked RSC slabs and the inner passing lanes 3%. The outer truck lanes carried over 3 times more trucks than inner lanes. The RSC slabs were mostly 200-223 mm thick and thus susceptible to fatigue damage. The overall performance of the RSC slabs (both CTS and 4x4 RSC materials) were similar and considered to be outstanding over 13 years with a large majority expected to survive many more years.

Iowa Experience on Local Calibration of AASHTOWare Pavement ME Design (PMED) for Jointed Plain Concrete Pavements

The AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG) pavement performance models and the associated AASHTOWare pavement ME design (PMED) software are nationally calibrated using design inputs and distress data largely obtained from National Long-Term Pavement Performance (LTPP) to predict Jointed Plain Concrete Pavement (JPCP) performance measures. To improve the accuracy of nationally-calibrated JPCP performance models for various local conditions, further calibration and validation studies in accordance with the local conditions are highly recommended, and multiple updates have been made to the PMED since its initial release in 2011, with the latest version (i.e., Ver. 2.5.X) becoming available in 2019. Validation of JPCP performance models after such software updates is necessary as part of PMED implementation, and such local calibration and validation activities have been identified as the most difficult or challenging parts of PMED implementation. As one of the states at the forefront of implementing the MEPDG and PMED, Iowa has conducted local calibration of JPCP performance models extending from MEPDG to updated versions of PMED. The required MEPDG and PMED inputs and the historical performance data for the selected JPCP sections were extracted from a variety of sources and the accuracy of the nationally-calibrated MEPDG and PMED performance prediction models for Iowa conditions was evaluated. To improve the accuracy of model predictions, local calibration factors of MEPDG and PMED performance prediction models were identified and gained local calibration experiences of MEPDG and PMED in Iowa are presented and discussed here to provide insight of local calibration for other State Highway Agencies (SHAs).

Adaptation and Calibration of the Faulting Model for Thin Concrete Pavements

Joint faulting is a pavement distress that affects the comfort level of jointed plain concrete pavements. The appearance of joint faulting usually occurs in areas of high traffic of trucks at high speed. Variables such as level of rainfall and the erodibility of the subbase increases the magnitude of this phenomenon. To predict joint faulting in Thin Concrete Pavements, the design software OptiPave2, launched in 2012, used the same model developed for the Mechanistic Empirical Pavement Design Guide (MEPDG), which uses an energy differential model. After 6 years of the release of the software and after 10 years since the construction of some thin concrete pavement projects, there are pavements with clear signs of joint faulting and others without. For this reason, the OptiPave2 model was reviewed and compared with field data, concluding that the faulting model needed to be adjusted This new model was calibrated with the data from existing concrete pavement projects.

Innovative test method for the reliable evaluation of joint sealants in concrete pavements

Joint sealants as indispensable filling systems in jointed plain concrete pavements (JPCP) are permanently exposed to various stresses during their service life, which often leads to a replacement of the sealing after approx. 7 to 10 years. Aside from seasonal unsteady climatic changes, the cyclical stresses caused by traffic and the ageing of joint sealants are especially significant. Considering the rising number of damages that occur within the overall "joint" system, an increased demand for a durable solution is requested as it is a relevant element for the life cycle costs of concrete pavements. In this context, a testing and ageing method was developed which comprises of the entire "joint" system, including the saw-cut concrete joint flanks, the primer as well as the joint sealant. This procedure depicts the decisive scenarios of in-situ stresses and allows the characterization of joint sealants. For this purpose, specimens were subjected to horizontal and vertical loads (static/cyclic) as well as to various ageing effects (temperature conditioning, UV-conditioning and freeze-thaw-cycles). After conditioning, a significant influence of the artificial ageing on the residual strength was observed in the tensile/shear tests. By comparing the artificially aged samples tested in the laboratory with extracted and in-situ aged samples, a reliable correlation was determined. Considering these system tests an initial approach was established which enables the evaluation of joint sealants in both unaged and artificially aged conditions on the basis of scientific parameters and limits.