No abstract

This paper reports the effects of carbon nanofibers (CNFs) on nanoscaled mechanical properties of cement composites. CNFs were added to cement composites at the filler loading of 0.2 wt % (by wt. of cement). Micrographs based on scanning electron microscopy (SEM) show that CNFs are capable of forming strong interfacial bonding with cement matrices. Experimental results using nanoindentation reveal that the addition of CNFs in cement composites increases the proportions of high-density calcium-silicate-hydrate gel (HD-CSH) compared to low-density CSH gel. It was also found that the inclusion of CNFs increases the compressive strength of cement composites.

The influence of nano-and microsilica addition on ordinary Portland cement (OPC) pastes has been studied in terms of hydration and microstructural properties. Three different combinations of nano-and microsilica mixes were used. A constant water-binder ratio of 0.35 was maintained throughout the experiment. All samples were tested for initial and final setting time and compressive strengths were determined at the age of 3, 7, 28, and 90 days of hydration. The hydration products were examined by SDT and XRD analysis at various curing ages. The inclusion of nano-and microsilica reduced the initial and final setting time significantly, increased the compressive strength of hardened cement paste after 7 days of hydration, and reduced the amount of calcium hydroxide in the hardened paste compared to mixes without these nanoparticles.

Metakaolin (MK) is a pozzolanic material, which is a dehydroxylated form of the clay mineral kaolinite. It is obtained by calcination of kaolinite clay at a temperature between 500°C and 800°C. In cement matrix, MK reacts with Ca (OH) 2 , to produce calcium silicate hydrate (CSH) gel. MK also contains alumina that reacts with Ca(OH) 2 to produce additional alumina-containing phases, including C 4 AH 13 , C 2 ASH 8 and C 3 AH 6 . This research aims to provide a better understanding of the effects of MK on the nanomechanical properties of the main phases present within the cement paste. Two different mixes were prepared, one control mix and the other one with 10 % MK (by cement weight). A constant waterbinder ratio of 0.4 was used for both the mixes. Fraction volumes determined from nanoindentation testing show an increase in the amounts of high-density CSH at the cost of low-density CSH gel in cement pastes containing 10 % MK.

This paper summarises an investigation into the behaviour of cement paste reinforced with 0·30% short multi-walled carbon nanotubes. Nanoindentation tests indicated that the addition of short nanotubes increased the amount of high-density calcium–silicate–hydrate compared with low-density calcium–silicate–hydrate gel. It was also observed that cement paste reinforced with short nanotubes had higher elastic modulus values than those of plain cement paste. Nanoscratch testing indicated that the presence of short nanotubes made the cement paste harder to penetrate into. The coefficient of friction values in cement paste reinforced with short nanotubes were found to be slightly higher than those in the plain cement paste.