Early-Age Autogenous and Drying Shrinkage Behavior of Cellulose Fiber-Reinforced Cementitious Materials

The objective of this study was to determine how the early-age shrinkage behavior of cementitious materials is affected by the addition of saturated cellulose fibers under sealed and unsealed conditions. The sealed condition simulates autogenous shrinkage exclusively while the unsealed condition introduces drying shrinkage, as well. Although the primary focus was to determine whether saturated cellulose fibers are suitable to mitigate autogenous shrinkage as an internal curing agent, evaluating their effect under drying conditions provided further insight into the overall shrinkage behavior of the composite material. At additions of 1% by mass of cement, the cellulose fibers were found to show significant drying shrinkage cracking control while providing some internal curing. In addition, early-age shrinkage test results were supplemented with a quantitative measure of fiber dispersion based on comparing theoretical and experimental values of the fiber volume fraction in hardened cementitious samples. Results indicated that improved dispersion leads to improved properties

Clinico-pathological characteristics of colorectal carcinoma at university teaching hospital, Nepal

Introductions: Colorectal cancer is a major health problem in developingcountries. The purpose of this study was to analyze the clinico-pathologicalcharacteristics of colorectal carcinoma at Patan hospital, Nepal.Methods: A retrospective chart review was done for patients operatedfor colorectal carcinoma at Patan Hospital from May 2004 to April 2012.Demographic information, chief complains, site of primary cancer, andhistological types were analyzed.Results: There were 73 patients (37 males and 36 females) with colorectalcarcinoma. The mean age was 52 years. There were 21 (28.77%) patients below 40 years of age. Patients with rectal carcinoma presented with bleeding per rectum in 69.70% and 60% of patients with colon cancer presented with pain abdomen. Rectum was involved in 31 (42.47%) and right colon in 30 (41.10%). Adenocarcinoma was seen in 72 (98.63%).Conclusions: The colorectal carcinoma is not only the disease of old age. Wehad 29% of our patients below 40 year. Rectum and right colon were equallyaffected.Keywords: bleeding, colorectal carcinoma, pain abdome

Studying Initiation and Growth of Shear Cracks in Reinforced Concrete Beams Using Full-Field Digital Imaging

The mechanisms which lead to shear failure of longitudinally reinforced concrete beams are complex and often misunderstood. In this paper, a combination of a special closed loop test technique and machine vision are applied to tests on two reinforced concrete beams failing in shear: one made of normal strength concrete and the second of high strength concrete. To control the progression of the shear crack, a closed-loop test technique was devised and employed such that the crack propagation was stable even during the post peak. To locate the crack and to measure the crack displacements, machine vision, a nondestructive measuring technique, was employed which gives full-field displacements of a viewed area. The displacement measurements are obtained by first grabbing digital images of the observed area at different stages of loading during the test. By comparing discrete subsets of the reference and target images using normalized cross correlation matching, the displacement fields of the images are calculated. Shear crack initiation and progression are monitored for the two beams tested through complete failure, and differences in the shear failures between reinforced beams made of normal and high strength concretes are noted

Conversion from Laparoscopic to Open Cholecystectomy

Introductions: With the advent of newer technology, the era of open surgery for gall bladder diseases has been preferably taken over by laparoscopic cholecystectomy. However, certain cases still require conversion to open surgery. In this review we aim to analyze the reason for conversion.Methods: This retrospective study was conducted at Patan Hospital, Patan Acdemy of Health Sciences, Nepal. All patients who underwent laparoscopic cholecystectomy from February 2009 to July 2012 were included in the study. File numbers of all the patients were obtained from operation room register. The patient files were analyzed for age, sex, duration of symptoms, liver function tests, ultrasound findings and the description in operation note for reason for conversion.Results: The age ranged from 12 to 81 years with mean age of patients 32.76 years and male to female ratio 1:2.9. The mean operating time was 65 minutes and average post operative hospital stay was 1.61 days. Out of 305 patients, 34 (11.14%) required open conversion. Factors esponsible for open conversion were dense fibrosis at Calots in 11 (3.6%), adhesions due to previous abdominal surgery in 6 (1.9%), uncontrollable bleeding in 5 (1.6%), bile duct injury in 4 (1.3%) cholecystoenteric fistula in 3 (0.9%), Mirizzi’s syndrome 2(0.6%).Conclusions: Adhesions at the calot’s triangle was the common reason for conversion from laparoscopic to open cholecystectomy.Keywords: adhesions, conversion, gallstone, laparoscopic cholecystectom

Analysis of corrugated shells

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Sanitary Engineering, 1959.Vita.Includes bibliographical references (leaves 147-148).by Surendra Tulsidas Shah.Sc.D

Influence of Clays on the Shrinkage and Cracking Tendency of SCC

The influence of different types of clay on the shrinkage and cracking tendency of fly ash modified self-consolidating concrete (SCCF) for the application of slipform paving were investigated in this study. The mortar phase of each mix was tested for autogenous shrinkage, total free shrinkage under drying and restrained shrinkage cracking. The mechanical properties (flexural strength, compressive strength, and modulus) were studied to supplement the results of the shrinkage and cracking tests. The plain SCCF mix was compared against the clay-modified SCCF mixes, as well as conventional SCC and slipform concrete (SFC) mixes. The results showed that the very early-age autogenous shrinkage of SCCF mortar was increased by the addition of clays due to adsorption effects. The effects of the clays on total shrinkage under long-term drying were found to depend mainly on the pozzolanic reactivity, but these effects were very slight at low dosages of about 1% by mass of binder. The early-age cracking tendency was aggravated by the clays composed of purified magnesium alumino silicate and metakaolin, but little influenced by the clay composed of kaolinite, illite and silica. Overall, the SCC mixture modified with both fly ash and a small amount of clay showed comparable shrinkage and early-age cracking performances as conventional SFC

Influence of Kaolinite Clay on the Chloride Diffusion Property of Cement-Based Materials

To constitute blended cement concrete with high chloride diffusion resistivity, the effects of kaolinite clay on the mechanical properties and chloride diffusivity of cement paste, mortar and concrete were investigated. Ordinary Portland cement was partially replaced by kaolinite clay at 0%, 1%, 3%, 5%, 7% and 9% by weight of cement. All blended cement-based samples were prepared using a w/c ratio of 0.5. The microstructure, workability, early-age and long-term flexural strength of pastes were tested. The chloride diffusivity of mortars was measured. And the compressive strength and chloride diffusivity of concrete were measured. Mercury Intrusion Porosimetry (MIP) was employed to evaluate porosity characteristics. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectra (EDS) were applied to investigate the micro morphology and chemical element distribution inside the cement matrix, and the rapid chloride migration (RCM) method was applied to test chloride diffusivity. The MIP test results show that the addition of clay improves the micro-pore structure in the cement paste and limits the introduction of chloride ions. SEM imaging suggests that the kaolinite clay is acting as both filler and accelerator of cement hydration. It is found that the addition of clay alters the water requirement of normal consistency and the setting time of cement, whereas it has little influence on the soundness. Compared to the control, the flexural strength of cement paste with 1% kaolinite clay increased by 30.41%, 39.04%, 36.27% and 38.32% at 1, 3, 7 and 90 days, respectively. The 28-day flexural strength only increased slightly. It is observed that the cement mortar with clay has lower chloride diffusion coefficient values compared to the plain mortar, the 28-day diffusion coefficient of chloride ion View the MathML source(DCl-) of cement mortar is decreased by 53.03% with 5% clay. The increase in compressive strength of the cement concrete with clay is 12%, 13.5%, and 28.4% compared to the control at 1%, 3% and 5% addition, respectively. The chloride diffusion coefficient of cement concrete decreases exponentially with the clay addition. The reduction of chloride diffusion coefficient of cement concrete is 8.68% and 18.87% at 1% and 5% clay, respectively. The 28-day compressive strength increases linearly with the chloride diffusion coefficient of the concrete

Surface Treatment of Cement-Based Materials with NanoSiO2

A dense surface structure of cement-based material is favorable for its resistance to the impacts of environment. In this work, effectiveness and mechanisms of the surface treatment of cement-based materials with nanoSiO2 of different states, that is, colloidal nanoSiO2 (CNS) and the in situ formed nanoSiO2 gel through the hydrolysis of its precursor of tetraethoxysilane (TEOS), by brushing and soaking techniques, were investigated. Results showed that both CNS and TEOS are capable of reducing the liquid and gaseous transport properties of hardened cement-based materials, although at a different extent. It revealed that the pozzolanic reactivity and the filler effect of nanoSiO2 are the main causes for the refining of the threshold size and the reduction of volume of the capillary pores, and they finally lead to a linearly reduction of the transport property. From this study, it can be reflected that surface treatment of cement-based materials with nanoSiO2 would be an optimal alternative of making concrete structure more durable

Influence of Purified Attapulgite Clays on the Adhesive Properties of Cement Pastes as Measured by the Tack Test

This study evaluates the influence of small additions of highly-purified attapulgite clays (0.2% and 0.5% addition by mass of cement) on the adhesive properties of cement pastes. Adhesive properties are measured by the tack test, a novel method of evaluating the rheological properties of granular materials. To better understand the results of the tack test as they pertain to cementitious materials, a highly concentrated material that is evolving due to thixotropic rebuilding and hydration, they are supplemented with a measure of the viscoelastic properties over time obtained through low-amplitude oscillatory shear rheometry. The influence of different preshear conditions and resting times (age of paste) on the adhesive properties are determined. Results show the tack test to be a suitable method for obtaining useful information about the adhesive properties and structural evolution of the material in the fresh state

Modification of Cement-Based Materials with Nanoparticles

This is a summary paper on the work being done at the Center for Advanced Cement-Based Materials at Northwestern University on the modification of cement-based materials with nanoparticles, specifically nanoclays, calcium carbonate nanoparticles, and nanosilica. The rheological properties of clay-modified cement-based materials are investigated to understand the influence of nanoclays on thixotropy. The influence of the method of dispersion of calcium carbonate nanoparticles on rate of hydration, setting, and compressive strength are evaluated. And an in-depth study on the mechanisms underlying the influence of nanosilica on the compressive strength gain of fly ash–cement systems is discussed. The motivation behind these studies is that with proper processing techniques and fundamental understanding of the mechanisms underlying the effect of the nanoparticles, they can be used to enhance the fresh-state and hardened properties of cement-based materials for various applications. Nanoclays can increase the green strength of self-consolidating concrete for reduced formwork pressure and slipform paving. Calcium carbonate nanoparticles and nanosilica can offset the negative effects of fly ash on early-age properties to facilitate the development of a more environmentally friendly, high-volume fly ash concrete