Carbon nanotubes (CNTs) are a virtually ideal reinforcing agent due to extremely high aspect ratios and ultra high strengths. It is evident from contemporary research that utilization of CNT in producing new cement-based composite materials has a great potential. Consequently, possible practical application of CNT reinforced cementitious composites has immense prospect in the field of applied nanotechnology within construction industry. Several repair, retrofit, and strengthening techniques are currently available to enhance the integrity and durability of concrete structures with cracks and spalling, but applicability and/or reliability is/are often limited. Therefore, there is always a need for innovative high performing concrete repair materials with good mechanical, rheological, and durability properties. Considering the mechanical properties of carbon nanotubes (CNTs) and the test results of CNT reinforced cement composites, it is apparent that such composites could be used conveniently as concrete repair material. With this end in view, the applicability of multiwalled carbon nanotube (MWNT) reinforced cement composites as concrete repair material has been evaluated in this study in terms of setting time, bleeding, and bonding strength (slant shear) tests. It has been found that MWNT reinforced cement mortar has good prospective as concrete repair material since such composites exhibited desirable behavior in setting time, bleeding, and slant shear.

Cementitious composites have high compressive strength and modulus of elasticity, but relatively low tensile strength, toughness and ductility. They are amenable to enhancement through nanotechnology due to the physical behavior and size of hydration products. Carbon Nanotube (CNT) is a very efficient reinforcing agent due to its extremely high aspect ratio and ultra-high strength. So, there is a high potential to utilize CNT in producing new cement based composite materials. In this study, a parametric experimental investigation was undertaken to determine optimum mix dosage of CNT for cement mortar. Different dosage rates of surface treated Multi-Walled Nanotubes (MWNT), water/cement ratios and plasticizer amounts (as surfactant for the MWNT) were investigated through compressive and flexural strength determinations. A mixing technique was proposed to address the issues related to dispersion of nanotubes within the cement matrix. The proposed mixing technique and design mix significantly enhanced the compressive and flexural strengths, as compared to control samples with no MWNT.

Application of nanoscale science to construction material has already begun. In recent times, various nanofibers have raised the interest of researchers due to their exceptional mechanical properties and high potential to be used as reinforcement within cement matrix. Carbon nanotube (CNT) is one of the most important areas of research in the field of nanotechnology. The size and exceptional mechanical properties of CNT show their high potential to be used to produce high performance next generation cementitious composites. In this study, an attempt has been made to investigate the effect of size of CNTs on compressive strengths of CNT reinforced cement composites. Seven different sizes of multiwalled nanotubes (MWNTs) were used to produce MWNT-cement composites. A trend was observed regarding the effect of nanotube size on compressive strength of composites in most cases. MWNT with outside diameter (OD) of 20 nm or less exhibited relatively better performance. Smaller MWNT can be distributed at much finer scale and consequently filling the nanopore space within the cement matrix more efficiently. This in turn resulted in stronger composites.

In recent times microbially induced calcite precipitation (MICP) has emerged in the cement and concrete industry as a pioneering approach to enhance concrete properties. This research was carried out with the intention to study the changed characteristics of masonry concrete, casted using brick aggregates modified by MICP. Biodeposition of CaCO3 on treated brick surfaces were detected via optical microscopy, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and energy-dispersive spectroscopy (EDS) analysis and analyzed through quantification of calcium carbonate. Absorption tests and mercury porosimetry tests were carried out to determine the changed brick characteristics. Finally, durability parameters of modified brick aggregate-concrete were determined through sorptivity test, rapid migration test (RMT), and compressive strength test. Experiments conducted on brick aggregates reveal that MICP methods were successfully executed leading to CaCO3 precipitation. Furthermore, the m...

The conventional external curing process requires supply of large amount of water in addition to mixing water as well as strict quality control protocol. However, in a developing country like Bangladesh, many local contractors do not have awareness and required knowledge on importance of curing which often results in weaker concrete with durability issues. Moreover, at times it is difficult to maintain proper external curing process due to nonavailability of water and skilled laborer. Internal curing can be adopted under such scenario since this method is simple and less quality intensive. Usually, naturally occurring porous light weight aggregates (LWA) are used as internal curing agent. However, naturally occurring LWA are not available in many countries like Bangladesh. Under these circumstances, Super Absorbent Polymer (SAP) can be utilized as an alternative internal curing agent. In this study, sodium polyacrylate (SP) as SAP has been used to produce internally cured concrete. Desorption isotherm of SP has been developed to investigate its effectiveness as internal curing agent. Test results showed that internally cured concrete with SP performed better in terms of both strength and durability as compared to control samples when subjected to adverse curing conditions where supply of additional water for external curing was absent.