Pore structure characteristics, modulation and its effect on concrete properties: A review

As inorganic rigid waterproof materials with excellent substrate compatibility, non-toxicity, harmless, and deep penetration depth, cementitious capillary crystalline waterproof materials (CCCW) hold great potential for application in concrete structures. However, the formulations of commercially available CCCW are currently undisclosed, hindering the mechanism study of CCCW, which is not conducive to the development of more efficient and cost-effective CCCW materials. In this study, a new formulation of CCCW active chemicals was developed, consisting of calcium carbonate, sodium silicate, glycine, EDTA-4Na, and sodium acetate. The effectiveness of sodium acetate as a high-quality impermeable admixture to CCCW was explored to enhance the impermeability of the substrate. Subsequently, the fundamental performance of the coatings was subjected to further examination. After application of the coating, the impermeability and strength of the substrate were enhanced, and the fist impermeability strength reached 1.5 MPa. Micro characteristics testing indicated that the coated sample had a denser microstructure, resulting in an increase of calcium carbonate crystals and hydrated calcium silicate in the pores. The harmful pores (100–3000 nm) were transformed into less harmful or harmless pores (< 100 nm). The durability tests indicated a 12.37 % drop in carbonation area over 14 days, with an approximately 30 % drop in the Coulomb electric flux of chloride ions. 

Preparation and performance study of active chemicals in cementitious capillary crystalline waterproofing materials

A comprehensive review on the toughening technologies of cement-based materials: From multiscale materials to advanced processes

It is an important direction for the sustainable development of pavement to mix the discarded concrete blocks with gradation according to a certain proportion after crushing, cleaning and other technological processes, partially or completely replace aggregate, and then add cement, water, and so on to make recycled concrete for pavement paving, but the traditional evaluation model for the compressive strength (CS) of recycled concrete cannot meet the requirements of efficient calculation. To address such issues, the present research proposed to apply the firefly algorithm (FA) to optimize the random forest (RF) model. The results were demonstrated by comparing the consistency of predicted and actual values, and also by analyzing the correlation coefficient (R) and root-mean-square error (RMSE). Higher R values (0.9756 and 0.9328) and lower RMSE values (3.0752 and 6.4369) for the training and test sets present the reliability of the FA and RF hybrid machine learning model. To understand the influence law of input indexes on the output index, the importance and sensitivity of variables are further analyzed. The results displayed that effective water-cement ratio (WC) and nominal maximum recycled concrete aggregate size (NMR) have the greatest impact on the output variable, with importance scores of 2.5947 and 2.4315, respectively, while the change in the recycled concrete aggregate replacement rate (RCA) has a weak influence, with an importance score of 0.4695. Introducing FA to RF for the compressive strength modeling of recycled concrete can significantly improve the computational efficiency and accuracy.

Improvement of Computational Efficiency and Accuracy by Firefly Algorithm and Random Forest for Compressive Strength Modeling of Recycled Concrete

Dumbbell-shaped piezoelectric energy harvesting from coupled vibrations

Concrete is a typical porous material, in which the air voids entrained or entrapped during the mixing process have a significant impact on the material’s strength and durability. An automatic methodology based on digital image analysis was used to examine the influence of a novel mixing process with vibration on the entrapped air pore size and distribution of concrete in this paper. The volume of permeable spaces and porosity in hardened concrete are found to be greatly reduced when using the vibration mixing process compared to the reference concrete. Meanwhile, the quantity of air pores and their specific surface area are positively associated with the vibration acceleration, while the average equivalent pore diameter decreases. The findings of the analysis of variance (ANOVA) reveal that the population means for porosity, quantity, and pore size are significantly different when utilizing the vibration or non-vibration mixing processes. Furthermore, the pore size distribution curves show that the vibration mixing process significantly modified the pore structure by reducing the number of larger size pores and increasing the amount of small size pores. This may be attributed to a series of changes in the bubbles during the vibration mixing process. In addition, the findings of freeze-thaw resistance and water penetration resistance reveal that, owing to the vibration mixing process, the impermeability and durability of the concrete are significantly improved.

/pdf/estimating-the-effect-of-vibration-mixing-process-on-air-3df2ykar.pdf

Estimating the Effect of Vibration Mixing Process on Air Pore Size Distributions in Concrete Using Digital Image Analysis

The reuse of construction and demolition waste has become vitally important because of the requirements of environmental protection and sustainable development. The vibration mixing process is a new technology and novel method that improves the performance of concrete by optimizing the mixing process without changing constituents. This study discusses the 100% recycled and multi-recycled coarse aggregates concrete using the vibration mixing process and investigates the fresh and hardened properties. The results show that the recycled and multi-recycled concrete using the vibration mixing process experienced obviously higher compressive strength than that of non-vibration mixing process. At 120 days, the compressive strength of all mixtures surpassed the target strength (40 MPa), except for the multi-recycled concrete with the non-vibration mixing process. More importantly, the compressive strength of the recycled and multi-recycled concrete using vibration mixing was larger than the previous-generation concrete using non-vibration mixing. Another interesting finding was that the coefficient of variation of compressive strength using vibration mixing was smaller and the concrete quality was better and more stable. The splitting tensile strength of recycled and multi-recycled concrete was also investigated and discussed. In addition, the results of t-tests show that vibration mixing has a significant influence on the compressive and splitting tensile strength of recycled and multi-recycled concrete. It is expected that the vibration mixing process could be a more efficient way to help the wide application of recycled and multi-recycled concrete.

/pdf/preparation-of-recycled-and-multi-recycled-coarse-aggregates-2vj7iutt.pdf

Preparation of Recycled and Multi-Recycled Coarse Aggregates Concrete with the Vibration Mixing Process

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Papers

Estimating the Effect of Vibration Mixing Process on Air Pore Size Distributions in Concrete Using Digital Image Analysis

Preparation of Recycled and Multi-Recycled Coarse Aggregates Concrete with the Vibration Mixing Process