Production, functionalization and application of carbon materials.

The work of this thesis was structured into 2 main activities: (1) to devise a surface functionalization technique for commercial carbon fibres (CFs) based on lignin precursor developed under the European Union FP7 Project “Functionalized Innovative Carbon Fibres Developed from Novel Precursors with Cost Efficiency and Tailored Properties” (FIBRALSPEC), grant agreement No. 604248. (2) To perform the exploration of low cost carbon fillers for application to polymer composites. 1st chapter presents a general introduction of the different carbon materials and their applications. 2nd chapter is concerned with the existing commercial carbon fibre manufacturing techniques and precursors. A small portion on the surface modification techniques is also added in this chapter. The 3rd chapter deals with the production techniques and limitations of Carbon nano tubes as a filler for the application to composites. A brief introduction on biochar materials has been added as well. The 4th chapter deals with functionalization study of commercial carbon fibres and lignin based carbon fibres. Commercial carbon fibres T700 were purchased from Toray, Japan to study the surface modification through low pressure oxygen plasma at Polito. Treatment parameters in an oxygen environment such as holding time (1~10 minutes), plasma power (100~200 W), flow rate (250 Standard Cubic Centimeters) and plasma chamber pressure (53 Pa) were set. Morphology of the carbon fibres before and after plasma treatment was studied through Field Emission Scanning Electron Microscopy (FESEM). Chemical nature of the functional groups formed on the carbon fibres surface after the treatment was studied through Fourier Transform Infrared (FTIR) spectroscopy and atomic percent was quantified through X-Ray Photoelectron Spectroscopy (XPS). Raman spectroscopy was carried out to study the structural changes in the carbon fibres. Wettability test was carried out to study the interaction of the surface functional groups with epoxy matrix. Tensile strength of the CFs was determined after the plasma treatment to ensure optimum mechanical performances of the treated fibres in the subsequent composites. In order to ensure the effectiveness of the plasma treatment the same samples were studied after six months of storage in ambient conditions. On the basis of the obtained results from the activities above, optimum plasma treatment parameters such as treatment time, plasma power, oxygen flow rate, plasma chamber pressure were singled out and applied on the lignin based carbon fibres. The lignin based CFs were plasma treated for 5 minutes at 100 W and 200W at a flow rate of 250 SCCM and 53 Pa plasma chamber pressure. Surface morphology was studied through FESEM. Plasma treated fibres showed canals and pits on the surface. The fibre started to damage at a plasma power of 200W. Also the oxygen pickup reduced at this treatment power as depicted by the XPS analysis. The 200 W, 5 minutes treatment was identified as an upper limit for the treatment parameter. The treated fibres were shredded finely and dispersed in epoxy resin using an overhead mixer to produce composites. Mechanical and tribological analysis was carried out and compared with the neat epoxy and untreated CFs composites. The plasma treated carbon fibre composites outperformed their counterparts. Based on the observations we recommended low pressure oxygen plasma treatment for the surface modification of the lignin based carbon fibres intended for commercial use. To further support our recommendations we produced carbon fibers from waste cotton clothes in Polito and applied the same treatment to them. The temperature profile for the thermal treatment was deduced from thermogravimetric analysis of cotton fibres in argon environment. XPS and FTIR analysis was carried out to ensure the absence of any impurity in the cotton fabrics. Carbonization process was carried out in a Carbolite furnace (TZF12/65/550) at the temperatures of 400o C, 600o C and 800o C for one hour in nitrogen environment at a ramp rate of 15o C/minute. The sample prepared at 800o C was selected to study the plasma treatment due to its more ordered structure and high carbon content as depicted by the Raman and XPS analysis respectively. The carbon fibres were treated with oxygen plasma at 100 W and 200 W for 5 minutes. Surface morphology and structure of the treated CFs were studied via FESEM and Raman spectroscopy. Surface of the treated fibres showed pits and canals confirming the action of the plasma elements while a degradation of the ID/IG ratio in the Raman spectra evidenced the effects of the plasma elements on the structure of the CFs. The functional groups on the surface of the plasma treated CFs were studied through X-Ray Photoelectron Spectroscopy and Fourier Transform Infrared spectroscopy. Chemical groups like alcohols, carboxyl and carbonyl were found on the surface of the treated CFs. BET analysis showed that surface area of the fibers increased after treatment. The plasma treated CFs retained higher amount of the epoxy resin in the wettability test. The plasma treated fibres were applied in composites. Epoxy based composites were fabricated with the pristine and treated CFs in 1% and 3% by weight. Mechanical and tribological analysis was carried out on all composites. The composites of the plasma treated fibres showed superior mechanical and tribological properties when compared to their untreated CFs counterparts. Morphology of the mechanical and tribological specimen were studied with FESEM to investigate the interaction of the filler with the matrix. Above results supported our earlier argument and low pressure oxygen plasma was recommended as a suitable treatment for the modification of the carbon fibres. The 2nd part of the thesis emphasizes the application of cheap precursor based carbon materials for the tailoring of composites properties. In recent years, low-cost carbons derived from recycled materials have gained a lot of attention for their potentials as filler in composites and in other applications. The electrical, frictional and mechanical properties of polymer composites can be tailored using different percentages of these fillers. In the Carbon lab at Polito we synthesized carbon nano materials (CNMs) from waste polyethylene bags in two different morphologies namely carbon nano beads (CNBs) (P1) and a mix of carbon nano tubes (CNTs) and carbon nano beads (P2) using chemical vapour deposition (CVD) technique by varying the carrier gas pressure. Morphology of the CNMs were studied through FESEM and their purity through Thermogravimetric Analysis (TGA) and Raman spectroscopy. Epoxy based composites were fabricated using these CNMs as filler in 1% and 3 % by weight. Mechanical properties and tribological properties were compared with the epoxy composites of commercial Multi Walled Carbon Nano Tubes (MWCNT). It is observed that the in house generated CNMs composites show overall better mechanical and tribology properties compared to the neat epoxy and the commercial MWCNTs based composites. Morphology of the composites was analysed through FESEM to study the interaction of the filler with the matrix that lead to improved performances. A model on the fracture behaviour was proposed on basis of FESEM analysis. Chapter 6 is concerned with this activity. In chapter 7, the maple based biochar has been explored as a cheap alternative filler to enhance the polymer properties. In this regard, the mechanical, tribological and electrical behavior of composites with two types of biochar based on maple wood namely biochar and biochar HT were investigated and compared with those of a composite containing multiwall carbon nanotubes. HT is heat treated at 900o C in nitrogen at 1 hour. Superior mechanical properties (ultimate tensile strength, Young modulus and tensile toughness) were noticed at low biochar concentrations 2~4 wt. %). Biochar based composites showed equivalent tribology properties to the composites fabricated with MWCNTs. Furthermore, dielectric properties in the microwave range comparable to low carbon nanotubes loadings can be achieved by employing larger but manageable amounts of biochar (20 wt. %) rending the production of composites for structural and functional application cost-effective. Conclusive remarks and future plans are compiled in chapter 8

Effect the Depth of Shearhead on the Behavior of Reinforced Concrete Flat Plate Slabs

This research presents an experimental study of effect the depth of shearhead on the behavior of  reinforced concrete flat plate slabs. Three reinforced   concrete slab specimens were casted and tested under static load. The effect of different section depth of shearhead has been discovered through studying its impact on the load-deflection behavior, ultimate capacity, cracking load, failure mode, stiffness, ductility and energy absorption of tested specimens. The result appeared that the specimen with large section height of collar shearhead gives an increase in ultimate capacity and first crack  about 83.5% and 34.6% respectively  over reference specimen So (without  shearhead).Also, the  reduction in stiffness  at failure of specimen CS8  is 82.7%  ,its clear more than  that of specimen  CS7, in comparison  with  it's  stiffness  at 25% . The  increasing  in energy  absorption was about (127.7%) of specimen  with large section height in comparison with  reference  specimen. It is concluded that the loading capacity, stiffness, ductility and energy absorption increased with increasing section depth of shearhead

Efficiency of Injection Method in Repairing of Normal Strength and Reactive Powder Reinforced Concrete Beams

The study aims to ensure the possibility of returning the strength of reinforced concrete beams to their original strength as a result of repairing work using epoxy injection method. Four different samples were poured and tested, the main variables in this study are the compressive strength in addition to the longitudinal steel reinforcement ratio and the other parameters are kept constant such as shear reinforcement (ø10@100 mm) and the dimension (180 ×250×1200). The test results showed that the ultimate strength of repaired beams approached greatly to the original beams strength. There is also an improvement in the ductility and stiffness of tested beams. Also, there is a decreasing in toughness of repaired beams in comparison with the original beams

Behavior of Reinforced Concrete Slabs Using Different Amounts of Steel Fibers

In this research, the effect of steel fibers on the punching shear characteristics of concrete slabs has been studied. Three specimens were poured and tested, one of them poured without steel fibers, and the others two specimens were poured with two different percentages of steel fibers (0.5% and 1%) of total volume. The effect of adding steel fibers has been discovered through studying its impact on the load-deflection behavior, ultimate capacity, cracking capacity, failure mode, ductility and energy absorption of tested specimens.It is concluded that the loading capacity, deflection, ductility and energy absorption increased with increasing steel fibers ratio. Also, the stresses at slab-column connection have been reduced

Punching Shear Strength Characteristics of Flat Plate Panels Reinforced with Shearhead Collars: Experimental Investigation

This paper presents an experimental investigation on the punching shear strength of reinforced concrete flat plate slabs with shearhead collars. Eight reinforced concrete slab specimens were casted and tested under static load test, the load was applied at the center of slab by 100x100 mm steel column. The effect of the shapes, diameter and number of stiffeners has been discovered for shearheads through studying its effect on the load-deflection behavior, ultimate capacity, cracking load, failure mode, stiffness, ductility and energy absorption of tested specimens. The experimental results indicates that using square shearhead had achieved a slight increase in punching shear strength about 3% over that circular shearhead using the same surface area. Also, utilize 550 mm shearhead diameter will contribute to increase the punching shear strength about 14.5%. The increase in the number of stiffeners in specimen (CS4) had reduced the ultimate punching shear capacity by 20.3% over reference specimen. The first crack was decreased from 12.5kN to 7.5kN, when increases the number of stiffeners from one to two. The cracking load was increased with the increase of the diameter of circular shearhead from 10kN to 15Kn in specimens of 336mm and 550mm respectively. The specimen with 336mm diameter and 30mm height circular shearhead achieved 427 kN.m energy absorption, it is higher than the energy absorption of reference specimen by 2.6%. Also, using two stiffeners improved the energy absorption by 110.2% higher than the specimen with one stiffener

Torsional Behavior of Hybrid Reinforced Concrete Box Girders Composed of Conventional Concrete and Modified Reactive Powder Concrete

This paper investigates experimentally the torsional behavior of hybrid reinforced concrete box beams composed of conventional concrete at side walls and modified reactive powder concrete at top and bottom flanges. Hybrid reinforced concrete members is used extensively to deal with the members strength requirements related to flexural, shear and torsion in structural systems. The torsion failure is an undesirable failure because it's occurred in a brittle nature, it is necessary to avoid this type of failure in the earthquake areas. Three reinforced concrete box beams with dimensions (300x300x1200) mm of (width x height x length) respectively and interior hollow dimensions (140x140)mm were cast and tested to failure by using two opposite cantilevers arms which contribute in transferring the torque to the central part of the box beam. One of the beams was poured with conventional concrete, second beam with modified reactive powder concrete and third beam was poured as a hybrid member. Experimental data on ultimate capacity, cracking torsional loads, failure pattern and twisting angle for each of the box beams were gained. The experimental results show that the ultimate torsional strength value of hybrid box beam higher than conventional concrete beam by about (58) % and lower than modified reactive powder concrete specimen by about (40.75)%. Keywords: Hybrid reinforced concrete, conventional concrete, modified reactive powder concrete and torsion

Elective induction for pregnancies at or beyond 41 weeks of gestation and its impact on stillbirths: a systematic review with meta-analysis

<p>Abstract</p> <p>Background</p> <p>An important determinant of pregnancy outcome is the timely onset of labor and birth. Prolonged gestation complicates 5% to 10% of all pregnancies and confers increased risk to both the fetus and mother. The purpose of this review was to study the possible impact of induction of labour (IOL) for post-term pregnancies compared to expectant management on stillbirths.</p> <p>Methods</p> <p>A systematic review of the published studies including randomized controlled trials, quasi- randomized trials and observational studies was conducted. Search engines used were PubMed, the Cochrane Library, the WHO regional databases and hand search of bibliographies. A standardized data abstraction sheet was used. Recommendations have been made for input to the Lives Saved Tool (LiST) model by following standardized guidelines developed by the Child Health Epidemiology Reference Group (CHERG).</p> <p>Results</p> <p>A total of 25 studies were included in this review. Meta-analysis of 14 randomized controlled trials (RCTs) suggests that a policy of elective IOL for pregnancies at or beyond 41 weeks is associated with significantly fewer perinatal deaths (RR=0.31; 95% CI: 0.11-0.88) compared to expectant management, but no significant difference in the incidence of stillbirth (RR= 0.29; 95% CI: 0.06-1.38) was noted. The included trials evaluating this intervention were small, with few events in the intervention and control group. There was significant decrease in incidence of neonatal morbidity from meconium aspiration (RR = 0.43, 95% CI 0.23-0.79) and macrosomia (RR = 0.72; 95% CI: 0.54 – 0.98). Using CHERG rules, we recommended 69% reduction as a point estimate for the risk of stillbirth with IOL for prolonged gestation (> 41 weeks).</p> <p>Conclusions</p> <p>Induction of labour appears to be an effective way of reducing perinatal morbidity and mortality associated with post-term pregnancies. It should be offered to women with post-term pregnancies after discussing the benefits and risks of induction of labor.</p

Microwave characterization of polymer composite based on Biochar: A comparison of composite behaviour for Biochar and MWCNTs

In this work, Biochar is used as a filler in Epoxy resin for composite preparation. The electrical characteristics of composites are analyzed in function of different filler percentages. Results obtained are compared with composites based on multi-wall carbon nanotubes

STRUCTURAL BEHAVIOR OF HYBRID REINFORCED CONCRETE COUPLED BEAMS CONTAINING REACTIVE POWDER CONCRETE AND HIGH STRENGTH CONCRETE

Reactive powder concrete and high strength concrete have superior mechanical and structural properties, however, the major drawback of this new construction material is its high cost compared to traditional concrete. This study presents an experimental investigation on the structural behavior of hybrid rectangular cross section (coupled) reinforced concrete beams poured with normal and high strength concrete (HSC) at compression chord, normal strength concrete (NSC) at ribs, and reactive powder concrete (RPC) at tension chord. The experimental work consists of pouring and testing four specimens with dimensions (1100mm length, 100 mm width, and 400 mm height). First specimen, rectangular solid normal concrete beam for comparison with specimens, second specimen, coupled beam poured with normal strength concrete at top chord, and two other specimens of coupled beams cast with high strength concrete with two compressive strengths (50 MPa and 70 MPa) at top chord. The effect of top chord concrete type at each specimen on ultimate load capacity, energy absorption, deflection and cracking load are studied in this investigation. Experimental results showed that the ultimate load carrying capacity and energy absorption increased to 76.9 % and 108.33 % respectively, compared with the solid specimen and recorded a reduction in deflection values through loading life and cracking load when using higher compressive strength of high strength concrete in compression chord in addition to reactive powder concrete in tension zone