Maw Tien Lee

Use of waste rubber as concrete additive

For resource reutilization, scrap tyres have long been investigated as an additive to concrete to form ‘Rubcrete’ for various applications and have shown promising results. However, the addition of rubber particles leads to the degradation of physical properties, particularly, the compressive strength of the concrete. In this study, a theoretical model was proposed to shed light on the mechanisms of decrease in compressive strength due to the addition of rubber particles as well as improvement in compressive strength through modification of particle surfaces. The literature suggests that the compressive strength can be improved by soaking the rubber particles in alkaline solution first to increase the inter-phase bonding between the rubber particles and cement. Instead, we discovered that the loss in compressive strength was due to local imperfections in the hydration of cement, induced by the addition of heterogeneous and hydrophobic rubber particles. Microscopic studies showed that the rubber particles disturbed the water transfer to create channels, which were prone to cracking and led to a loss in the compressive strength. Unexpectedly, no cracking was found along the surfaces of the rubber particles, indicating that the bonding strength between the rubber particles and cement phases was not the critical factor in determining the compressive strength. Therefore, a theoretical model was proposed to describe the water transfer in the Rubcrete specimens to explain the experimental data. In the model, the local water available for hydration (Q) is: Q=-A slv/6πν, where Q, A slv, and ν are mass flow rate (kg s-1), Hamaker constant (J), and dynamic viscosity (m2 s-1), respectively. By maximizing the quantity Q and, in turn, the Hamaker constant A slv, the compressive strength could be improved. The Hamaker constant A slv for water film on rubber particle surfaces was smaller than that for the hydrated cement particles; the water transfer rate was lower in the presence of rubber particles because the Hamaker constant A slv for water film on rubber particle surfaces was smaller than that on the hydrated cement particles. Thus, the compressive strength of Rubcrete could be improved by increasing the Hamaker constant of the system. This was achieved by increasing the refractive indices of the solids (n s). The refractive indices of materials increase with increases in functional groups, such as OH and SH on the surface. The model provided a possible mechanism for the efficacy of treating rubber particles with NaOH in improving the compressive strength. By using NaOH solution treatment, an oxygen-containing OH group was formed on the rubber surface to increase the Hamaker constant of the system, leading to higher compressive strength. Based on this mechanism, a novel method for modification of the rubber particles was also proposed. In this process, the rubber particles were partially oxidized with hot air/steam in a fluidized bed reactor to produce the hydrophilic groups on the surface of the particles. Preliminary results obtained so far are promising in accordance with the theory.

Improving rubber concrete by waste organic sulfur compounds

In this study, the use of crumb tyres as additives to concrete was investigated. For some time, researchers have been studying the physical properties of concrete to determine why the inclusion of rubber particles causes the concrete to degrade. Several methods have been developed to improve the bonding between rubber particles and cement hydration products (C—S—H) with the hope of creating a product with an improvement in mechanical strength. In this study, the crumb tyres were treated with waste organic sulfur compounds from a petroleum refining factory in order to modify their surface properties. Organic sulfur compounds with amphiphilic properties can enhance the hydrophilic properties of the rubber and increase the intermolecular interaction forces between rubber and C—S—H. In the present study, a colloid probe of C—S—H was prepared to measure these intermolecular interaction forces by utilizing an atomic force microscope. Experimental results showed that rubber particles treated with waste organic sulfur compounds became more hydrophilic. In addition, the intermolecular interaction forces increased with the adsorption of waste organic sulfur compounds on the surface of the rubber particles. The compressive, tensile and flexural strengths of concrete samples that included rubber particles treated with organic sulfur compound also increased significantly.

NUCLEATE POOL BOILING IN A CONFINED SPACE

Nucleate pool boiling of pure water and dilute aqueous sodium lauryl sulfate (SLS) solutions within a confined space between heated and unheated horizontal-parallel surfaces has been investigated under atmospheric pressure. The electrically heated lower surface is made of a sheet of stainless steel 304 with the dimension of 145 × 22 × 0.05 mm and the unheated upper plate is a stainless steel cylinder with a diameter of 20 mm. Periphery of the confined space is open and the size of the gap can be varied from 0 to 10 mm. Experimental results show that with the size of the gap between 0.3 and 3 mm, the heat transfer coefficient may increase to as much as 200 percent of those measured for conventional pool boiling. The addition of surfactant has no significant influence on the heat transfer coefficient in this case. Based on the experimental results, the microlayer evaporation with fluid flow driven by the gradient of disjoining pressure is discussed and considered as an important heat transfer mechanism for ...

Regenerable adsorbent for removing ammonia evolved from anaerobic reaction of animal urine.

The waste gas evolved from biodegradation of animal urine contains ammonia causing environmental concerns. A new and effective method for removing ammonia from such waste gas using reactive adsorption is presented. In the process, activated carbon impregnated with H2SO4(H2SO4/C) is employed. Ammonia in the waste gas reacts with H2SO4 on the adsorbent instantaneously and completely to form (NH4)2SO4. The H2SO4/C adsorbent is high in NH3 adsorption capacity and regenerable. The NH3 removal capacity of this regenerable adsorbent is more than 30 times that of the adsorbents used normally in the industry. The spent H2SO4/C is regenerated by flowing low-pressure steam through the adsorbent bed to remove the (NH4)2SO4 from the adsorbent. The regeneration by-product is concentrated (NH4)2SO4 solution, which is a perfect liquid fertilizer for local use. Re-soaking the activated carbon with H2SO4 solution rejuvenates the activity of the adsorbent. Thus the H2SO4/C can be reused repeatedly. In the mechanism of this reactive adsorption process, trace of H2O in the waste gas is a required, which lends itself to treating ammonia gas saturated with moisture from biodegradation of animal urine.

TEE EFFECT OF EXTENDED THIN FILM EVAPORATION DURING TEE CONSTANT DRYING RATE PERIOD

ABSTRACT The extended thin film evaporation is analyzed during the constant drying rate period. The extended thin film is defined as the liquid film which the disjoining pressure dominates the fluid flow field and works as the driving force of replenishing the evaporating liquid. The results of the analysis show that the extended thin film evaporation can compensate the reduction of evaporation rate due to the increase of dry spots and keep the evaporation rate nearly constant. Experimental data in the literature are in good agreement with the results of this work. This implies that the extended thin film evaporation may be an important part of the mechanism for drying.

TEE EFFECIS OF EXTENDED THIN FILM EVAPORATION AND EXPWNAL DIFFUSION RESISTANCE DURING THE CONSTANT DRYING RATE PERIOD

ABSTRACT Extended thin film evaporation with external diffusion resistance is analyzed for the constant rate period of the drying process, in which a polar liquid evaporates from porous bodies made of glass. The extended thin film is defined as the Liquid film in which the disjoining pressure dominates the fluid flar field and works as the driving force replenishing the evaporating Liquid. The results of the analysis shows that due to the existence of the evaporating thin Liquid film, the evaporation fran the extended thin film can compensate the reduction of evaporation rate caused by the increase of the dry spots and keep the drying rate the same as or even greater than that of the completely wetted surface. The external diffusion resistance makes the vapor concentration near the porous solid surface remain constant and therefore keeps

The Effect of the Disjoining Pressure on the Surface Evaporation of a Porous Medium

ABSTRACT The behavior of surface evaporation of a porous medium is investigated experimentally. A theoretical analysis is used to describe the experimental results in this work. Quartz sand(10–20 mesh) is packed as the porous medium. Pure water with electric resistance greater than 10 MΩ and aqueous solution with various concentration of sodium sulfate are used as working liquid in the experiments. Electric light radiation is used as the heat source. Free convection is used in the experiments. The results of the experiment show that the concentration of the salt has great influence on the rate of surface evaporation. A model of microlayer evaporation is developed to predict the drop of evaporation rate. The agreement of experimental results and theoretical results show that the evaporation of the microlayer, driven by the gradient of the disjoining pressure, as well as the interface of the liquid surface curvature due to meniscus effects is important.

ON THE INTERLINE EVAPORATING REGION OF A WETTING THIN FILM

ABSTRACT The extent interline of evaporating region is analyzed for polar liquid film, with the disjoining pressure expressed by Pd = B ln(t) + A. An average effective evaporation is defined for this region and expressed as a simple equation. The results of analysis show that the average effective evaporation rate varies with the relative vapor pressure and so does the length of the interline evaporating region. The increase in relative vapor pressure will make the evaporation from the wetting film more significant.

On the Improvement of Fiber Reinforced Concrete through Surface Modification of Polypropylene by Grafting Method

Polypropylene (PP) fiber reinforced concrete is an important composite. In order to improve the mechanical properties of PP fiber reinforced concrete, polyacrylamide (PAM) was grafted onto the PP surface by the UV irradiation to enhance the hydrophilic property of PP in this study. IR spectra showed the existence of carboxylic acid functional groups on the treated PP surface. AFM images depicted that the treated PP surface had the lower height fluctuation, roughness, and had the acicular appearance. Contact angles of the treated PP were reduced in comparison with that of the original PP. All of these experimental results gave the evidences that PAM had been successfully grafted onto the treated PP surface. Furthermore, OM images depicted that the treated PP adhered to cement hydrate products (C-S-H) more tightly than that of the original PP did. We therefore expect that PP grafted with PAM can enhance mechanical properties of PP fiber reinforced concrete.

BOILING OF MIXTURES IN A NARROW SPACE

Abstract Nucleate pool boiling of binary mixtures composed of water and normal propyl alcohol (NPA) within a narrow space between heated and unheated horizontal-parallel surface has been investigated under atmospheric pressure. The electrically heated lower surface is made of a sheet of stainless steel 304 with the dimension of 145 x 22 x 0.05 mm and the unheated upper plate is a stainlesssieel cylinder with a diameter of 20 mm. The periphery of the confined space is open and the size of the gap can be varied from 0 to 10 mm. Experimental results show that the heat transfer coefficient of nucleate pool boiling of binary mixture in a narrow space is much greater than that of conventional nucleate pool boiling. It is due to the evaporation of a thin liquid film under the deformed bubble. Experimental results also show that mass diffusion effect is important in both nucleate pool boiling in a narrow space and in conventional nucleate pool boiling. Based on the experimental results, the microlayer evaporation...