• Advances in environmental research
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• v.1 no.1
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• pp.83-96
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• 2012

The water sludge is generated from the treatment of water with alum. Disposing of sludge again to the streams raises the concentrations of aluminum oxides in water, which has been linked to Alzheimer's disease. The use of water treatment plant (WTP) sludge in manufacturing of constructional elements achieves both the economical and environmental benefits. Due to the similar mineralogical composition of clay and WTP sludge, this study investigated the complete substitution of brick clay by sludge incorporated with some of the agricultural and industrial wastes, such as rice husk ash (RHA) and silica fume (SF). Three different series of sludge to SF to RHA proportions by weight were tried, which were (25: 50: 25%), (50: 25: 25%), and (25: 25: 50%), respectively. Each brick series was fired at 900, 1000, 1100, and $1200^{\circ}C$. The physical and mechanical properties of the produced bricks were then determined and evaluated according to Egyptian Standard Specifications (E.S.S.) and compared to control clay-brick. From the obtained results, it was concluded that by operating at the temperature commonly practiced in the brick kiln, a mixture consists of 50% of sludge, 25% of SF, and 25% of RHA was the optimum materials proportions to produce brick from water sludge incorporated with SF and RHA. The produced bricks properties were obviously superior to the 100% clay control-brick and to those available in the Egyptian market.

• Computers and Concrete
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• v.19 no.2
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• pp.153-159
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• 2017

In this study, the strength properties of alkali-activated silica fume (SF) mortars were investigated. The crushed limestone sand with maximum size of 0-5 mm and the sodium meta silicate ($Na_2SiO_3$) used to activate the binders were kept constant in the mortar mixtures. The mortar specimens using the replacement ratios of 0, 25, 50, 75 and 100% SF by weight of cement together with $Na_2SiO_3$ at a constant rate were produced in addition to the control mortar produced by only cement. Moreover, the mortar specimens using the replacement ratio of 4% titanium dioxide ($TiO_2$) by weight of cement in the same mixture proportions were produced. The prismatic specimens produced from eleven different mixtures were de-moulded after a day, and the wet or dry cure was applied on the produced specimens at laboratory condition until the specimens were used for flexural strength ($f_{fs}$) and compressive strength ($f_c$) measurement at the ages of 7, 28 and 56 days. The $f_{fs}$ and $f_c$ values of mortars applied the wet or dry cure were compared with the results of control mortar. The findings revealed that the $f_c$ results of the alkali activated 50% SF mortars were higher than that of mortar produced with Portland cement only. It was found that the $f_{fs}$ and $f_c$ of alkali-activated SF mortars cured in dry condition was averagely 4% lower than that of alkali-activated SF mortars cured in wet condition.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.141-152
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• 1994

The results of an experimental study on the development and the evaluation of lightweight and high strength composites utilizing by-products and calcium silicates for construction materials are presented in this paper. The composites using early strength portland cement, by-Products( f1y ash, silica fume), silica powder, quick lime, gypsum, A1 powder and fibers(PAN-derived CF, alkali-resistance GF) were prepared using various mixing conditions. As the test results show, PAN-derived CF and alkali-resistance GF were suitable for rein-forcing fiber of the composites. And the mechanical properties,such as compressive tensile flexural strength, and toughness of Lt. Wt. fiber reinforced calcium silicates cement comp-osites were improved by increasing the fly ash and silica fume contents, and fiber contents, especially by increasing fiber contents the toughness of the composites were remarkably in-creased. Also, compressive tensile flexural strength,and toughness of the composites rein-forcing PAN-derived CF were higher than those of the composites reinforcing alkali-resistance GF..

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.23-30
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• 2008

UHPC has high performance, high strength and excellent mechanical properties. Moreover UHPC(Ultra High Performance Cementitious Composite) has advantage to reduce cross section under the same load compared with other kinds of concrete. But silica fume which is imported from foreign country has a abundant portion in UHPC mixture in comparison with normal concrete. This is one of the main reason to raise the construction cost. Superior mechanical properties of UHPC due to the optimum filling composition can be changed by replacing the very fine ingredient. The purpose of this research is to grasp the characteristic of UHPC which silica fume and silica flour is replaced with limestone powder. This experiment can be divided into three classes according to the kinds of replacement. The compressive strength and flow of all types were measured and microstructure and hydration phenomena for comparing RPC were analyzed by SEM, XRD, NMR method. As a result, the replacement can be considered to be effective by for the decrease of the UHPC structure construction cost and improvement of the fresh UHPC.

• Computers and Concrete
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• v.17 no.6
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• pp.801-814
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• 2016

An alternative type of building system with masonry units is extensively used nowadays to reduce the emission of CO2 and embodied energy. Long-term performance of such structures has become essential for sustaining the building technology. This study aims to assess the strength and durability properties of concrete prepared with unprocessed bagasse ash (BA) and silica fume (SF). A mix proportion of 1:3:3 was used to cast concrete cubes of size $100mm{\times}100mm{\times}100mm$ with various replacement levels of cement and tested. The cubes were cast with zero slump normally adopted in the manufacturing of hollow blocks. The cubes were exposed to acid attack, alkaline attack and sulphate attack to evaluate their durability. The mass loss and damages to concrete for all cases of exposures were determined at 30, 60, and 90 days, respectively. Then, the residual compressive strength for all cases was determined at the end of 90 days of durability test. The results showed that there was slight difference in mass loss before and after exposure to chemical attack in all the cases. Though the appearance was slightly different than the normal concrete the residual weight was not affected. The compressive strength of 10% bagasse ash (BA) as a replacement for cement, with 10% SF as admixture resulted in better strength than the normal concrete. Hence concrete with 10% replacement with BA along with 10% SF as admixture was considered to be durable. Besides solid concrete cubes, hollow blocks using the same concrete were casted and tested simultaneously to explore the possibility of production of masonry units.

• Structural Engineering and Mechanics
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• v.88 no.2
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• pp.141-157
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• 2023

In the present paper, the effect of recycled aggregates on the rheological and mechanical properties of self-consolidating concrete is investigated experimentally and numerically. Hence, the specimen with two types of recycled aggregates, i.e., known and unknown resistance origins, are utilized for the studied specimens. The experiments in this study are designed using the Box-Behnken method, which is one of the response surface methods. Input variables in mixtures include silica fume in the range of 5-15% as a percentage substitute for cement weight and recycled coarse and fine aggregates in the range of 0-50% for both series of recycled materials as a substitute for natural materials. The studied responses are slump flow, V funnel, compressive strength, tensile strength, and durability. The results indicate that the increase in the amount of recycled aggregates reduces the rheological and mechanical properties of the mixtures, while silica fume effectively improves the mechanical properties. In addition, the results demonstrate that the fine recycled aggregates affect the total response of the concrete significantly. The results of tensile and compressive strengths indicate that the mixtures including 50% recycled materials with known resistance origin demonstrate better responses up to 8 and 10% compared to the materials with unknown resistance origins, respectively. Recycled materials with a specific resistance origin also show better results than recycled materials with an unknown resistance origin. Durability test results represent those concretes containing recycled coarse aggregates have lower strength compared to recycled fine aggregates. Also, a series of mathematical relationships for all the responses are presented using variance analysis to predict mixtures' rheological and mechanical properties.

• Journal of the Korea Institute of Building Construction
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• v.24 no.1
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• pp.23-34
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• 2024

This research aims to assess the flexural bonding efficacy of polymer-cement composites(PCCs) in mending cracks within reinforced concrete(RC) structures. The study involved infilling PCCs into cement mortar cracks of varying dimensions, followed by evaluations of enhancements in flexural adhesion and strength. The findings indicate that the flexural bond performance of PCCs in crack repair is influenced by the cement type, polymer dispersion, and the polymer-to-binder ratio. Specifically, the use of ultra-high early strength cement combined with silica fume resulted in an up to 19.0% improvement in flexural bond strength compared to the application of ordinary Portland cement with silica fume. It was observed that the augmentation in flexural strength of cement mortar filled with PCCs was significantly more dependent on the depth of the crack rather than the width. Furthermore, PCCs not only acted as repair agents but also as reinforcement materials, enhancing the flexural strength to a certain extent. Consequently, this study concludes that PCCs formulated with ultra-high early strength cement, various polymer dispersions, silica fume, and a high polymer-to-binder ratio ranging from 60% to 80% are highly effective as maintenance materials for crack filling in practical settings.

• Journal of Preventive Medicine and Public Health
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• v.28 no.1 s.49
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• pp.43-57
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• 1995

In order to study the effect of welding fume exposure upon the pulmonary function test, we examined 131 shielded arc welding workers, and 152 $CO_2$ arc welding workers as cases and 177 control workers for their general characteristics, and forced vital capacity (FVC), forced expiratory volume in one second $(FEV_{1.0})$, forced expiratory volume in one second as a percent of FVC $(FEV_{1.0}%)$, and maximal mid-expiratory flow (MMF) were obtained from the spirogram. In shielded arc welding group and $CO_2$ arc welding group, FVC, $FEV_{1.0},\;FEV_{1.0}%$, and MMF were significantly decreased than control group, especially marked in the MMF finding. The distribution of workers below normal range was as follows. in the shielded arc welding group, 2 workers(1.5%) for FVC, 17 workers(13.0%) for $FEV_{1.0}$, 5 workers(3.8%) for $FEV_{1.0}%$, 28 workers(21.4%) for MMF, and in the $CO_2$ arc welding group, 3 workers(2.0%) for FVC, 25 workers(16.4%) for $FEV_{1.0}$, 8 workers(5.3%) for $FEV_{1.0}%$, and 37 workers(24.3%) for MMF, and significant increase by exposure duration was found in MMF. The distribution of workers who had ventilation impairment was as follows: 5 workers(3.8%) for obstructive type, 2 workers(1.5%) for restrictive type in the shielded arc welding group, and 7 workers(4.6%) for obstructive type, 2 workers(1.3%) for restrictive type, and 1 worker(0.6%) was combined type of the $CO_2$ arc welding group. In the respect of these results, the significant pulmonary function and ventilatory impairment were observed in welding fume exposed workers who had not abnormal finding in chest X-ray, and MMF considered as the most sensitive pulmonary function index by welding fume exposure. Therefore even if it is hard to doing pulmonary function test in the first health examination of workers according to the Industrial Safety Health Act in the welding fume exposure workers, it is desirable to consider doing PFT. Also evaluating the ventilation impairment, it is necessary, to observe the change of MMF that marker of effort-independent portion.

• The Journal of the Korea Contents Association
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• v.14 no.4
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• pp.389-396
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• 2014

This study was conducted as the basic research for the replacement of Blast Furnace Slag, Red Mud, Silica Fume, etc., with cement as a solution to the problems arising from the global warming caused by the generation of $CO_2$, and conducted the experimental review to examine the feasibility of matrix having properties identical to those of cement by using the Blast Furnace slag, Red mud, Silica fume, and alkali-activator. For this, by using the the inorganic binder, such as Blast Furnace Slag, Red Mud, Silica Fume, etc., and NaOH, $Na_2SiO_3$ and others as the cement substitute material, the strength characteristic according to the mixture time variation was performed in the tentative experiment. Based on the preceding experiment, this study performed the experiment to analyze the strength properties of hardener through the curing by air-dry temperature, curing by temperature in water, coating curing, and Korean paper curing. For the water curing at $80^{\circ}C$, the compressive strength and flexural strength were found to be the most excellent at the age of the 28th day, and furthermore, it was found that the non-cement hardener could be made, which is considered to affect the production of eco-friendly concrete.

• Environmental Mutagens and Carcinogens
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• v.23 no.3
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• pp.85-93
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• 2003

Welders working in a confined space, like in the shipbuilding industry, are at risk of being exposed to high concentrations of welding fumes and developing pneumoconiosis or other welding-fume exposure related diseases. Among such diseases, manganism resulting from welding-fume exposure remains a controversial issue, as the movement of manganese into specific brain regions has not been clearly established. Accordingly, to investigate the distribution of manganese in the brain after welding-fume exposure, male Sprague Dawley rats were exposed to welding fumes generated from manual metal arc stainless steel (MMA-SS) at concentrations of $63.6{\pm}4.1$ $mg/m^3$ (low dose, containing 1.6 $mg/m^3$ Mn) and $107.1{\pm}6.3$ $mg/m^3$ (high dose, containing 3.5 $mg/m^3$ Mn) total suspended particulates for 2 hrs per day, in an inhalation chamber over a 60-day period. Blood, brain, lungs and liver samples were collected after 2 hr, 15, 30, and 60 days of exposure and the tissues analyzed for their manganese concentrations using an atomic absorption spectrophotometer. Although dose- and time-dependent increases in the manganese concentrations were found in the lungs and livers of the rats exposed for 60 days, only slight manganese increases were observed in the blood during this period. Major statistically significant increases in the brain manganese concentrations were detected in the cerebellum after 15 days of exposure and up until 60 days. Slight increases in the manganese concentrations were also found in the substantia nigra, basal ganglia (caudate nucleus, putamen, and globus pallidus), temporal cortex, and frontal cortex, thereby indicating that the pharmacokinetics and distribution of manganese inhaled from welding fumes would appear to be different from those resulting from manganese-only exposure.