Abstract
Decoupling the individual effects of multiwalled carbon nanotubes (MWCNTs) and surfactants when used as reinforcement materials in cement-based composites is aimed in this study. Powder MWCNTs were dispersed in deionized water using different types of surfactants as chemical dispersing agents and an ultrasonic tip processor. Cement pastes with carbon nanotubes additions of 0.15% by mass of cement were produced in two steps: first, the MWCNT/surfactant dispersions were combined with the mixing water, and then, cement was added and mixed until a homogeneous paste was obtained. Mechanical properties of the pastes cured at 7 days were measured, and their fracture behavior was characterized using the linear elastic finite element analysis. It was found that the reinforcing effect of MWCNT was masked by the negative effect of surfactants in the cement matrix; nevertheless, nanotubes were capable of increasing both stress and strain capacity of the composite by controlling the crack propagation process at the tip of the crack.
Highlights
To guarantee adequate crack propagation control, multiwalled carbon nanotubes (MWCNTs) must be well dispersed in the cement matrix [4], bridging the correct phases. is means that if MWCNTs agglomerate around individual hydrates instead of bridging neighboring ones, they will not have any effect on the stress distribution within the composite [5]. is is why the use of chemical dispersing agents, such as surfactants, is of prime importance to produce MWCNT-reinforced cement-based composites
Some literature reports have shown decreases in mechanical properties of cement-based matrices. is behavior has been attributed to agglomeration phenomena of MWCNT when used in high volumes [14], to the presence of functional groups on the surface of the nanotubes able to interact chemically with the hydration reaction [12], or even to the presence of fine aggregates in the matrix for the case of mortars [15]. ese conflicting reports are still a matter open for discussion [16], and the issue is a subject of several experimental and numerical studies [17,18,19,20,21,22,23]. is work aims at quantifying the reinforcing efficiency of MWCNT/surfactant dispersions, separating the effects induced by surfactants in the mechanical properties of the matrix from those induced by MWCNT
Results and Discussion is section presents the characterization of the raw materials used to produce cement pastes blended with MWCNT/surfactant dispersions; the individual e ect of surfactants and MWCNT on the mechanical properties of the pastes is presented and discussed
Summary
To guarantee adequate crack propagation control, MWCNTs must be well dispersed in the cement matrix [4], bridging the correct phases. is means that if MWCNTs agglomerate around individual hydrates instead of bridging neighboring ones, they will not have any effect on the stress distribution within the composite [5]. is is why the use of chemical dispersing agents, such as surfactants, is of prime importance to produce MWCNT-reinforced cement-based composites. It is not clear that what is the extent of the reinforcing efficiency of MWCNT, but it has been found that small amounts of nanotubes increase the flexural strength of Advances in Civil Engineering cement-based matrices [8], identifying a correlation between their aspect ratio and reinforcing efficiency [9,10,11]. Additional parameters such as modulus of rupture [12], fracture energy, and fracture toughness [13] have been identified to increase with the presence of MWCNT in the matrix. Some literature reports have shown decreases in mechanical properties of cement-based matrices. is behavior has been attributed to agglomeration phenomena of MWCNT when used in high volumes [14], to the presence of functional groups on the surface of the nanotubes able to interact chemically with the hydration reaction [12], or even to the presence of fine aggregates in the matrix for the case of mortars [15]. ese conflicting reports are still a matter open for discussion [16], and the issue is a subject of several experimental and numerical studies [17,18,19,20,21,22,23]. is work aims at quantifying the reinforcing efficiency of MWCNT/surfactant dispersions, separating the effects induced by surfactants in the mechanical properties of the matrix from those induced by MWCNT
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