Mechanical properties of concrete containing recycle concrete aggregates and multi-walled carbon nanotubes under static and dynamic stresses

The growing demand for natural aggregates in the construction industry has motivated researchers to utilize recycled concrete aggregates (RCA) to preserve the natural resources and provide sustainable structure. However, the use of RCA in concrete applications has revealed defects in performance with low strength and rapid collapse under static and dynamic loads, respectively. Thus, the objective of present research is to improve these properties by using multi-walled carbon nanotubes (MWCNT). This study involves evaluating the fresh and hardened properties of recycled aggregate concrete (RAC) modified with different levels of MWCNT. The study involves RCA (i.e., 0 %, 25 %, 50 %, 75 % and 100 %) as replacement for natural aggregates, and MWCNT (i.e., 0.05 %, 0.1 % and 0.25 %) as weight of cement. The experimental testing consists of 240 specimens prepared from different mixtures. Workability is assessed using slump tests. Mechanical properties including static compressive strength and dynamic impact resistance are evaluated at 7 and 28 days. Experimental results show that incorporating MWCNT at all levels significantly reduces the slump values for all specimens. On the other hand, the compressive strength is increased by adding MWCNT to the concrete samples. The compressive strength of the RAC increased by as much as 70 % when modified with MWCNT. Furthermore, the inclusion of MWCNT is found to significantly increase the impact resistance of RAC specimens with percentage developments reaching approximately 11–508 % and 110–679 % at 7 and 28 days, respectively, at both first crack and failure stages. The dosage of 0.1 % MWCNT is shown to exhibit the highest percentage enhancement in impact resistance among the other nano levels. The failure patterns and cracks propagation are presented as well

Nanomaterials characteristics and current utilization status in rigid pavements: mechanical features and sustainability. a review

Rigid pavements are recognized as one of the most widely means by which people and goods move around for popular aims and certain objectives. Nowadays, the utilization of rigid pavements is becoming an urgent demand and an increasing need, for these pavements require less maintenance and less renovation compared to other types. As a result, the structures are becoming more economical and more profitable. However, during its lifespan, normal rigid pavement is facing many challenges and difficulties. Its initial erection cost is extremely higher compared to asphalt pavements, its higher sensitivity to dynamic stresses, its higher susceptibility to temperature variations caused cracking, and further to its greater contribution to global carbon dioxide emissions. Past works of literature have been dealing with these drawbacks through employing efficient materials as alternatives to replace cement and/or aggregates in the concrete pavement mixtures. In recent years, the application of nanomaterials has received considerable interest to enhance the mechanical performance of construction materials which can also be available for rigid pavement constructions. Despite its poor performance in the fresh conditions, the addition of nanomaterials to rigid pavements has shown significant improvements in static properties like compressive and tensile strengths; dynamic properties like fatigue flexure and impact strengths. This enhancement is mainly due to the role of nanomaterials which acting as nano reinforcements and nanofillers within the concrete pavement blends. This review paper presents and discusses the behavior of nano-modified rigid pavements under different external loads. The effect of nano-SiO2, nano-CaCO3, nano-Al2O3, nano-TiO2, nano-clay and nanotubes are focused. Besides, as a promising sustainable structure, the influence of nano-SiO2 on the hardened properties of recycled rigid pavement is deeply discussed (both in normal and supplementary cementitious structures). Mechanical characteristics and optimal percentages are reviewed. A better comprehension of the characteristics of the nanostrengthening rigid pavements can provide an academic base for future works and engineering applications of developed concrete materials in the pavement construction industry

Nanomaterials in recycled aggregates concrete applications: mechanical properties and durability. A review

The use of recycled aggregates concrete (RAC) contributes effectively to reduce CO2 emissions from concrete manufacturing process while also protecting natural resources by utilizing existing available concrete as an aggregates source for a new one. Studies on the behaviour of RAC have revealed negative effects on concrete strength and microstructure development, resulting in deterioration of mechanical and durability properties. As a result, numerous practical studies have been implemented to enhance the RAC properties using various treatment techniques such as chemical, physical and heating treatments. However, most of these techniques are ineffective compared to conventional concrete applications due to poor mechanical performance of RAC, insufficient environmental requirements, and prolonged treatment times. Recently, the use of nanomaterials has been given significant concern in RAC research. Their nano-sized particles can help to reduce micropores formation by acting as a filling agent to produce a high-density microstructure, thereby enhancing the mechanical properties and durability of RAC. This had led to a wide range of studies being published on improving RAC properties by using nanomaterials. However, relatively few literatures had been conducted on the effects of different types of nanomaterials on the performance of RAC exposed to various types of loads and various external environmental impacts. Besides, the conditions used by authors in these literatures limit comparisons, and in some cases contradictory findings are observed. Thus, this paper aims to bridge the knowledge gap between researchers. This would allow the potential of nanotechnology in innovations to be applied in appropriate areas of RAC applications to benefit the general public good. This paper aims to provide a critical review and comprehensive conclusions on the performance of nano-modified RAC under external loads, environmental impacts and other various conditions. The effects of nanomaterials on the compressive, tensile, and flexural strength of RAC are discussed. The nanomaterials considered are nano-SiO2, nano-CaCO3, nano-TiO2, nano-Clay, nano-Al2O3, and nano-Carbon. Durability characteristics including water absorption, chloride penetration, fire exposure, abrasion resistance, acid and carbonation diffusions are extensively discussed. Microstructure characteristics using SEM, XRD, EDS, and micro-hardness of nano-modified RAC are addressed as well