Simulation of Concrete in Winter with Self-Limiting Heating Band

In order to investigate the temperature distribution and cracking risk of concrete in winter under the combined action of heating zone and air layer, the analytical calculation method of early age concrete temperature field of concrete component under the combined action of self-limiting temperature band, cement hydration and air layer was established by taking concrete prism with self-limiting temperature band as an example. The model is applied to calculate and analyze the temperature distribution of concrete under different boundary conditions and different additional thermal field modes. The results show that: Under the conditions of internal layout, surface layout and thermal insulation layer outside the formwork, all components reach the critical strength after heating and curing for three days, which indicates that the heating band can provide temperature conditions for concrete curing in winter. Comparing the temperature field of different layout positions of heating belt, the uniformity of temperature field of heating belt outside the formwork is better than the other two layout methods.

Effect of Fibre Reinforcement on Creep in Early Age Concrete

This research analyses the strain behaviour of fibre-reinforced concrete (FRC) in the event of a creep episode. The analysis of creep experienced by FRC specimens during the test reflects better performance than that predicted by the EHE-08 standard. The authors propose a formulation for the evaluation of creep strain undergone by FRC. During the research, the evolution of the modulus of elasticity of FRC after a creep episode is analysed. After the test campaign, it can be concluded that FRC loaded at an earlier age stiffens after a creep episode. After the creep test is completed, the delayed elastic strain undergone by FRC is analysed and it is observed that FRC loaded at an earlier age undergoes less deformation. The authors propose a formulation for the evaluation of the delayed elastic strain undergone by FRC after a creep episode.

Measurement of Dry and Autogenous Shrinkages and Thermal Strain of Early Age Concrete Pavement

(1)Background: Early-age concrete shrinkage induces stress that impact the cost and service life of concrete pavements. (2)Methods: In this study, strain measurements of field slabs were conducted and a methodology was presented that independently derived autogenous, drying, and thermal shrinkages in the initial stages of concrete placement. Total strain was measured according to five different environmental conditions and shrinkage strain was calculated for each condition. (3)Results: By measuring the strain of the slab and the specimen, the drying shrinkage strain was measured to be approximately 54% better than that by the conventional non-stressed cylinder method because it was possible to measure the drying shrinkage strain at the surface rather than in the middle part of the slab along its depth direction. When the water-to-cement ratio increased (35→40%), there was a considerable reduction (317με→82με) of autogenous shrinkage strain for the concrete at 28 days of age. Furthermore, calculation of stress-dependent strain allowed the presentation of more intuitive and accurate results. (4)Conclusion: As the measurement of independent shrinkage occurrence is possible, the consequent calculated result of the stress-dependent strain acting on real slabs will facilitate improvement in the construction quality, reduction in the development of defects in the concrete structure, and increase in the service life.

Use of Methylcellulose-Based Pellet to Enhance the Bacterial Self-Healing of Cement Composite

In this study, a new type of bacterial carrier using methylcellulose was presented, and its applicability to self-healing concrete has been explored. Methylcellulose, the main component of a 2 mm pellet-shaped carrier, can remain stable in alkaline environments and expand in neutral or acidic environments. These properties allow bacteria to survive in the high-alkaline and high-pressure environments of early age concrete, and the number of bacteria increases rapidly in the event of cracks, accelerating crack closure. The results show that the survival rate of bacterial spores inside the mortar was increased, and the pellet provides an enhanced biological anchor suitable for bacterial activity, bacterial growth, and mineral precipitation. Further, the results indicate an improved self-healing efficiency compared with mixing bacteria directly into the cement composite.