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In recent decades, there have been initiatives to incorporate carbon nanomaterials (CNMs) into cement composites, particularly graphene oxide (GO), carbon nanotubes, graphite (GP), and mild carbon (MC). Nevertheless, little is known about how these CNMs interact with the cement matrix itself. In this research, the impact of CNM incorporation at high temperatures (250, 500, 750, and 1,000°C) on cement’s mechanical characteristics and microstructure was investigated. Nine mixes were created with the CNM content (0.1 and 0.3%) being taken into consideration. The microstructure of the CNM composites was further investigated using X-ray diffractometry, thermogravimetry, derivative thermogravimetry, digital microscopy, and micro-computed tomography (micro-CT). Based on research observations, the study demonstrated that the mechanical properties of most specimens could be enhanced through the introduction of CNMs. The recommended proportions of GP-0.1, GO-0.1, and MC-0.1, in accordance with the weight of the binder, and the impact of the CNMs on the elastic modulus were also assessed. As a consequence, the CNM’s porous structure and apparent crack pattern were identified using microstructure analysis.

The focus of this research was to investigate the effects of graphene oxide (GO) on the microscopic composition, structure, pore size, and mechanical properties of GO-reinforced cement composites. Furthermore, the research explored the thermal behavior of GO-reinforced cement mortar at different elevated temperatures (250, 500, 750, and 1,000°C). This study considered three sets of GO-reinforced cement composites with 0.1, 0.2, and 0.3 wt% of GO (by weight of cement); the water–cement ratio in all the mixtures was 0.5. To characterize the chemical composition, microstructure, and hydration degree resulting from GO addition, X-ray diffraction, thermogravimetry, derivative thermogravimetry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and micro-computed tomography (Micro-CT) were used. The experimental results revealed that GO addition changed the microstructural composition and pore diameter distribution of the cement composite. The optimal amount of GO required for improving the mechanical properties of the cement composite under both unheated and heated conditions was identified to be 0.1 wt%. GO improves the cement matrices’ ability to bind with GO nanosheets, leading to compressive strength retention and decreased micro-cracking (computed by material and defected volume changes by Micro-CT analysis). This is primarily due to the hydration products. However, the optimal amount of GO can result in nanomaterial agglomeration, thus lowering the thermal resistance of the cement composite. Overall, the study identified GO as a nano-additive with the potential to improve the strength and toughness of the cement composites. Moreover, the effect of elastic modulus was also evaluated. As a result, the GO microstructure analysis revealed that it has a porous structure with a visible crack pattern.

Very-early-strength latex-modified concrete (VES-LMC) was developed for rapid repairs of distresses in concrete bridge decks and pavements, with the emphasis on early-age strength gain so that the repaired bridges and pavements can be opened to traffic within the time frame required in the specifications. However, there are two main concerns in the use of VES-LMC--early-age cracking and poor air void structure. The main objective of this study was to further improve VES- LMC to minimize early-age cracking and improve freeze-thaw durability, which included the use of fine fly ash (FFA) and calcium hydroxide (CH). Laboratory experiments were conducted on VES-LMC materials with cement replaced with FFA as well as CH, and various tests performed. Early-age drying shrinkages of VES-LMC containing both FFA and CH in the amounts evaluated in this study were smaller than that of VES-LMC with no replacements. It is expected that the use of FFA and CH in the range evaluated in this study will reduce the cracking potential of VES-LMC. Overall, the replacement of cement with FFA and CH improved the characteristics of entrained air void system, which will enhance the durability of VES-LMC against freeze-thaw damage. Scanning electron microscope and energy dispersive spectroscopy analysis indicate the primary mechanism of the generation of small sized air voids in concretes containing adequate amount of FFA and CH is the gas formation reaction between citric acid solutions and CH during concrete mixing. It is expected that the inclusion of adequate amounts of FFA and CH in VES-LMC will improve the performance of repaired bridge decks and pavements in terms of reduced cracking and improved freeze-thaw durability. Key words: air void structure, freeze and thaw, fine fly ash, rapid setting concrete. Le beton modifie au latex a prise ultra-rapide (BML-PUR) a ete concu pour reparer les dommages dus a l'usure sur les tabliers de pont et revetements en beton. Sa capacite a durcir rapidement a ete mise en avant, car elle permettait de rouvrir a la circulation les ponts et chaussees repares dans les delais requis. Cependant, l'utilisation d'un tel beton pose deux principaux problemes: l'apparition de fissures prematurees et une structure caracterisee par une mauvaise repartition des vides interstitiels. L'objectif principal de la presente etude a ete d'ameliorer les performances de ce type de beton afin de reduire au minimum l'apparition de fissures prematurees et de renforcer sa resistance dans le temps au gel-degel, a l'aide notamment de cendres volantes (CV) et d'hydroxyde de calcium (HC). Des essais en laboratoires ont ete realises sur des echantillons de BML- PUR dans lesquels le ciment a ete remplace par des CV et de l'HC et d'autres types d'essais ont effectues. Les retraits de sechage premature du BML-PUR contenant a la fois des CV et de l'HC, dans les quantites determinees dans la presente etude, etaient moins importants que ceux observes sur le BML-PUR uniquement compose de ciment. On s'attend a ce que l'utilisation de CV et d'HC, dans les intervalles de teneurs definis dans la presente etude, aura pour effet de reduire le risque de fissuration du BML-PUR. D'une maniere generale, le remplacement du ciment par des CV et de l'HC a permis d'ameliorer les caracteristiques des occlusions d'air formant les vides interstitiels a l'interieur du beton, ce qui renforcera la resistance dans le temps du BML-PUR au gel-degel. Une analyse au microscope electronique a balayage et une analyse dispersive en energie montrent que la reaction entre les solutions d'acide citrique et l'HC, qui se produit durant la preparation du melange de beton, constitue le principal mecanisme de formation des vides interstitiels de petite taille dans les betons contenant des quantites adequates de CV et d'HC. On s'attend a ce que l'ajout de quantites appropriees de CV et d'HC dans le BML-PUR ameliore a l'avenir les performances des tabliers de pont et revetements repares, en reduisant la fissuration du beton et en renforcant sa resistance dans le temps au gel-degel. [Traduit par la Redaction] Mots-cles: repartition des vides interstitiels, gel et degel, cendres volantes, beton a prise rapide., 1. Introduction The most frequent and serious distress type reported in jointed plain concrete pavement (JCP) in South Korea is spalling at transverse and longitudinal joints, primarily due to freeze [...]

Hydrodemolition is a method of surface preparation using high-pressure water jets. Hydrodemolition cutting depth is dependent on the length of time that the water jet is directed at the concrete surface that determines the depth of removal, and contact time is controlled at the robotic cutter. During hydrodemolition concrete removal, the cement matrix is removed from the aggregate. This paper describe on the test results of under-water hydrodemolition which was done on a prefabricated concrete basin. A very simple and economic method for repairing the damaged concrete structures is a using a sprayed concrete, which is some times called as shotcrete. This paper, also, describe on the test results of sprayed concrete for the rehabilitation of marine concrete structure.

This article examines the characteristics of shotcrete from the standpoint of resistance to plastic shrinkage cracking. The effects of 2%, 3%, and 4% replacement with colloidal silica (CS) with a 10-nm particle size on the performance of shotcrete was examined, as were the effects of addition of supplementary cement materials in combination with CS, such as silica fume (SF) and ultra-fine fly ash (UFFA). Plastic cracking was examined from three perspectives: its effect on strength development (especially at the initial stage), assessment of plastic shrinkage in accordance with the ASTM C1579, and related issues of bleeding and evaporation. Compressive and flexural strength tests were conducted to gain an understanding of the processes involved, and the Intelligent Crack Viewer FCV-30 was used to estimate crack widths. The results show that the replacement with CS increases the compressive and flexural strength during hardening, which increases its resistance to tensile shrinkage stresses. The practical assessment of cracks showed that a significant reduction in the width of plastic shrinkage cracks was also achieved. The combination of 4% SF and 2% CS significantly reduced the risk of cracking and improved strength characteristics. The application of CS reduced the effect of 20% UFFA on plastic cracking. [ABSTRACT FROM AUTHOR]