Effects of Pitch-Based Short Carbon Fibers on the Workability, Unit Weight, and Air Content of Mortar Composite

Abstract

Pitch is a viscoelastic polymer material consisting of aromatic hydrocarbons. It is used to produce carbon fibers with sheet-like crystal structures. The aim of the work presented in this paper was to evaluate the effects of pitch-based short carbon fibers on the workability, unit weight, and air content of freshly mixed mortar composite. Experimental investigation was carried out on five different types of mortar composite, including a control mortar. Four mortar composites were prepared including pitch-based short carbon fibers with 1–4% volume contents. The fresh mortar composites were tested to determine their slump, inverted slump cone flow (flow time, mass flow, and volume flow), unit weight, and air content. In addition, the correlation between the slump and flow time of various mortar composites was determined. It was found that the slump decreased with the increasing volume content of carbon fibers. The flow time of mortar composite increased, and therefore its mass flow and volume flow decreased with a greater volume content of carbon fibers. The slump was strongly correlated with the flow time, with a correlation coefficient of 0.9782. Furthermore, the unit weight of the fresh mortar composite decreased due to the incorporation of carbon fibers. However, amongst the different carbon fiber reinforced mortar composites, the mortar with 3% fiber volume content provided the highest unit weight. The air content results were consistent with the unit weight results. The change in air content of various mortar composites followed a trend reciprocal to that of unit weights. When the overall effects of carbon fibers were compared, it was observed that the fiber volume content higher than 3% resulted in a significantly low workability and provided a much lower unit weight with greater entrapped air content.

Performance and Cost-Effectiveness of Short Pitch-Based Carbon Fiber Reinforced Mortar Composite

“…CFRM4, which included 4% carbon fibers, had a lower workability compared with CFRM1 and CFRM2, which had 1% and 2% carbon fibers, respectively. This is because the higher surface area of the carbon fibers tends to restrain the mobility of the fresh mortar composite [ 42 , 56 ] due to increased water demand to entirely wet the constituent materials. Therefore, a comparatively high superplasticizer dosage was required to make CFRM4 workable.…”

“…Furthermore, the air content increased to a greater extent with the higher volume content of carbon fibers, as evident from Table 3 . This is because the presence of carbon fibers in the mortar impedes the movement of air voids to the surface during casting and compaction, thus entrapping them in the fresh composite [ 18 , 42 ]. However, it is evident from Table 3 that CFRM3 had the lowest air content.…”

“…However, all these improvements greatly depend on the workability of CFRM. A high workability enhances the degree of compaction and thus plays an important role in reducing the capillary pores and entrapped air voids in a mortar composite [ 18 , 42 ]. Excessive capillary pores were likely to exist in CFRM4 because it was too stiff due to its low workability, despite using a relatively high dosage of superplasticizer and the same amount (15%) of silica fume.…”

“…In contrast, the total mixing time was 4 min for the OPCM. The details of the mix procedure are given in [ 42 ].…”

Effect of carbon reinforcements on selected properties of mortar

“…The effects of short carbon fibers on the workability, unit weight and air content of blended mortar composite were evaluated by Safiuddin et al (2018), results showed that the overall effects of carbon fibers when the fiber volume per cent is higher than 3% lead to decreasing the workability and unit weight with higher entrapped air content (Safiuddin et al 2018).…”