Combined Effects of Set Retarders and Polymer Powder on the Properties of Calcium Sulfoaluminate Blended Cement Systems

This study investigates the effects of set retarders on the properties of polymer-modified calcium sulfoaluminate (CSA) and Portland cement blend systems at early and long-term ages. The fast setting of the cement blend systems is typically adjusted by using retarders to ensure an adequate workability. However, how the addition of retarders influences the age-dependent characteristics of the cement blend systems was rarely investigated. This study particularly examines the effects of retarders on the microstructure and strength development of polymer-modified CSA and Portland cement blend pastes and mortars from 2 h to 90 days. The macro- and microstructural properties are characterized by compression testing, powder X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy with energy dispersive spectroscopy. The test results reveal that the use of retarders delayed the strength development of the cement blend systems at the very early age by hindering the production of ettringite, which was cumulative to the delaying effect of polymer, but it increased the ultimate strength by creating denser and finer pore structures with the evolution of hydration products

Rheological properties of cement pastes with cellulose microfibers

The rheological properties of cement pastes prepared using kenaf-plant cellulose microfibers (CMFs), which was incorporated for the purpose of internal curing, were investigated. The main test variables are the length and mass fraction of the CMFs. CMFs of lengths of 400 ??m and 5 mm were included in the mixtures at 0.3, 0.6, 1, and 2 wt.% of the cement. Dry CMF particles were wetted with water to the fiber saturation point using vacuum filtration immediately before mixing. An optimum shearing protocol was designed to minimize the shear-induced structural breakdown of cement pastes with the CMFs under hysteresis loops of the shear strain rate. It consisted of an initial pre-shearing step at a high shear strain rate of 80 1/s, three acceleration and deceleration cycles with a maximum shear strain rate of 40 1/s, and a rest step before each acceleration. The mixtures??? flow curves were well fitted to the Herschel???Bulkley fluid model with a minimum coefficient of determination of 0.9993. The yield stress of cement pastes was at least 34.3% higher for longer CMFs at the same dose. However, the mixtures exhibited similar plastic viscosities with a coefficient of variation of only approximately 5.8%

Surface-Wave Based Model for Estimation of Discontinuity Depth in Concrete

In this paper, we propose an accurate and practical model for the estimation of surface-breaking discontinuity (i.e., crack) depth in concrete through quantitative characterization of surface-wave transmission across the discontinuity. The effects of three different mixture types (mortar, normal strength concrete, and high strength concrete) and four different simulated crack depths on surface-wave transmission were examined through experiments carried out on lab-scale concrete specimens. The crack depth estimation model is based on a surface-wave spectral energy approach that is capable of taking into account a wide range of wave frequencies. The accuracy of the proposed crack depth estimation model is validated by root mean square error analysis of data from repeated spectral energy transmission ratio measurements for each specimen

Applicability of Diffuse Ultrasound to Evaluation of the Water Permeability and Chloride Ion Penetrability of Cracked Concrete

This study aims to explore the applicability of diffuse ultrasound to the evaluation of water permeability and chloride ion penetrability of cracked concrete. Lab-scale experiments were conducted on disk-shaped concrete specimens, each having a different width of a penetrating crack that was generated by splitting tension along the centerline. The average crack width of each specimen was determined using an image binarization technique. The diffuse ultrasound test employed signals in the frequency range of 200 to 440 kHz. The water flow rate was measured using a constant water-head permeability method, and the chloride diffusion coefficient was determined using a modified steady-state migration method. Then, the effects of crack width on the diffusion characteristics of ultrasound (i.e., diffusivity, dissipation), water flow rate, and chloride diffusion coefficient are investigated. The correlations between the water flow rate and diffuse ultrasound parameters, and between the chloride diffusion coefficient and diffuse ultrasound parameters, are examined. The results suggest that diffuse ultrasound is a promising method for assessing the water permeability and chloride ion penetrability of cracked concrete

Concrete Crack Identification Using a UAV Incorporating Hybrid Image Processing

Crack assessment is an essential process in the maintenance of concrete structures. In general, concrete cracks are inspected by manual visual observation of the surface, which is intrinsically subjective as it depends on the experience of inspectors. Further, it is time-consuming, expensive, and often unsafe when inaccessible structural members are to be assessed. Unmanned aerial vehicle (UAV) technologies combined with digital image processing have recently been applied to crack assessment to overcome the drawbacks of manual visual inspection. However, identification of crack information in terms of width and length has not been fully explored in the UAV-based applications, because of the absence of distance measurement and tailored image processing. This paper presents a crack identification strategy that combines hybrid image processing with UAV technology. Equipped with a camera, an ultrasonic displacement sensor, and a WiFi module, the system provides the image of cracks and the associated working distance from a target structure on demand. The obtained information is subsequently processed by hybrid image binarization to estimate the crack width accurately while minimizing the loss of the crack length information. The proposed system has shown to successfully measure cracks thicker than 0.1 mm with the maximum length estimation error of 7.3%

Characteristics of GGBFS-Based Pervious Concrete Considering Rheological Properties of the Binder

To mitigate environmental challenges, such as urban flooding, noise pollution, and the urban heat island effect, pervious concrete has been developed. This research was intended to develop pervious concrete made from ground granulated blast furnace slag (GGBFS) to further decrease the environmental impact of the construction sector by reducing the content of ordinary Portland cement (OPC). The primary objective of the mix proportion was to maximize water permeability while meeting the required compressive strength. Two levels (60 and 100%) of OPC replacement by GGBFS were evaluated and compared to OPC-only concrete, and two target porosities (10 and 15%) were achieved by modifying the binder-to-aggregate ratio. CaO and CaCl2 were utilized as an activator and an accelerator, respectively, for the GGBFS only binder. Characteristics of the pervious concrete were determined with the compressive strength, porosity and water permeability test. Meanwhile, the effects of the rheological properties of binders on the water permeability and compressive strength of pervious concretes was evaluated. According to the results, the permeability of pervious concretes always exhibited a positive correlation with porosity, regardless of binder type. Although, the pervious concrete made with CaO-activated GGBFS has a lower compressive strength than the other two cases (60% GGBFS and only OPC), it still meets the minimum strength requirement. Based on the rheology studies of binder, it was found that, the adhesion force of the binder and the compressive strength of the pervious concrete decreases, as evaluated by rheology studies on binders. The CT scan revealed that when the adhesive force of the binder was weaker, the local porosity was higher (i.e., pore volume was larger) at the bottom of the specimen, which might be due to the limited consolidation and compaction of the binder between aggregate particles at the bottom due to its higher plastic viscosity

Shining Light on the Shadow: Full-round Practical Distinguisher for Lightweight Block Cipher Shadow

Shadow is a lightweight block cipher proposed at IEEE IoT journal 2021. Shadow’s main design principle is adopting a variant 4- branch Feistel structure in order to provide a fast diffusion rate. We define such a structure as Shadow structure and prove that it is al- most identical to the Generalized Feistel Network, which invalidates the design principle. Moreover, we give a structural distinguisher that can distinguish Shadow structure from random permutation with only two plaintext/ciphertext pairs. By exploiting the key schedule, the distin- guisher can be extended to key recovery attack with only one plain- text/ciphertext pair. Furthermore, by considering Shadow’s round func- tion, only certain forms of monomials can appear in the ciphertext, re- sulting in an integral distinguisher of four plaintext/ciphertext pairs. Even more, the algebraic degree does not increase more than 12 for Shadow-32 and 20 for Shadow-64 regardless of rounds used. Our results show that Shadow is highly vulnerable to algebraic attacks, and that algebraic attacks should be carefully considered when designing ciphers with AND, rotation, and XOR operations