Study On Mechanical Properties Of Multi-walled Carbon Nanotubes Reinforcing M140DSP Mortar

This paper studied the production and properties of M 140DSP mortar based on commercially acceptable materials and field-curing,and proposed a new mixing technics—TSMT(three-speed mixing technics).In order to decrease the brittleness of M140DSP mortar,multi-walled carbon nanotubes(MWNTs) was added into it as a reinforcement.Appling the ordinary mechanical test machines,uniaxial tensile and compress properties were studied.And the electronic mechanical test machine was applied to study the three-point bending properties.The SEM,EPMA and ESEM examinations of fracture surface showed the main re-inforcing mechanisms.The results shown:1 The mixtures mixed by TSMT have better workability and at 28-day age,the compressive strength reaches 150MPa.At the same mix proportion and curing,the CT mixed paste is denser than the TSMT mixed paste,and the flow uniformity of the CT mixed paste is worse than that of the TSMT mixed paste.At 28-day age,the compressive strength of the DSP mortar mixed by TSMT reaches 146MPa,showed 44.2%higher than that of the DSP mortar mixed by CT.By the wedge-splitting sections photos and ESEM images,it can be observed that TSMT fines the pore size distribution and decreases the porosity of the DSP mortar not only in macroscale but also in microscale.The TG curves are also different,the weight loss of DSP mortar mixed by TSMT is less than that of DSP mortar mixed by CT.2 The higher the strength of DSP mortar above 100MPa is,the less the fracture energy is.3 The failure modes of ultra-high strength about C100～150 obtained by other researchers is splitting and exploding(Ⅰtype,two ends restricted).In this paper the compressive failure modes of M140 mortar prism are:Ⅰtype,two ends restricted;Ⅱtype,one end restricted and the other splitted;Ⅲtype,splitting failure.Splitting failure may be the true failure mode of prism under pure compressive load.4 With the addition of two different A-MWNTs dispersions including carbonyl disper-sions of A-MWNTs(C-A-MWNTs) and aqueous dispersions of A-MWNTs (A-A-MWNTs) with the addition of 0.01 wt%A-MWNTs were utilized to obtain enhanced mechanical properties with respect to plain M140.The results indicated that the use of A-MWNTs dispersions allows increasing compressive strength and flexural strength by 8.4% and 5.4%,respectively for the C-A-MWNTs-M140,and by 15.9%and 20.7%for the A-A-MWNTs-M140,respectively.5 At the same failure mode and position,with the addition of 0.02wt%(cement weight) PVA fiber,the reinforcement of PVA fiber on the bending properties and the prism compressive stress are not distinct.PVA fiber only makes the uniaxial tensile stress and strain improved 39.3%and 101.7%with respect to plain M140DSP mortar.But for long walled multiwalled-carbon nanotubes L-MWNT-1030,not only makes the prism compressive stress and ultimate strain improved 68.7%and 24.9%respectively,and the bending load and displacemen improved 35.8%and 14.9%respectively,but also makes the uniaxial tensile stress and ultimate strain improved 72.7%and 73.8%,and the stress-strain curve has a non-linear segment.But applying the same production technics,the increments of the strengthes and strains of the L-MWNT-1030-M140DSP mortar composites do not increase with the fiber content(the maximum L-MWNT-1030 content is 0.2%wt cement) increased.6 The re-inforcing mechanisms of carbon nanotubes are:fiber pullout and debond;fiber bridge;fiber pin and microfilling effect.In order to make full use of the re-inforcing mechanisms of carbon nanotubes,carbon nanaotubes should be well distributed in the form of net in the defects of matrix.