PubMed · 14768286
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Moisture and hidden problems.. https://pubmed.ncbi.nlm.nih.gov/14768286/
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This research was undertaken to address environmental concerns associated with industrial solid waste and to reduce cement consumption in geotechnical engineering. It specifically investigates the feasibility of using steel slag (SS) and silica fume (SF) as partial substitutes for ordinary Portland cement (OPC) in soil stabilization. The effects of SS, SF, OPC, and initial moisture content on the unconfined compressive strength (UCS) of stabilized soil were investigated through single-factor experiments and response surface methodology (RSM). The results show that SS and SF can synergistically enhance the strength of stabilized soil, although their interaction effect was not statistically significant within the investigated ranges. Compared with soil stabilized solely with OPC, the addition of 18 % SS and 10 % SF reduced OPC consumption by 3 % without compromising strength. Microstructural and compositional analyses further revealed that SS mainly supplied calcium- and silica-bearing components, while SF provided highly reactive silica and micro-filling effects, jointly promoting hydration reactions and improving the compactness of the stabilized soil matrix. As a result, more hydration products were formed in the OPC/SS/SF-stabilized soil than in the OPC-stabilized soil, which contributed to pore filling and strength enhancement. This study provides useful guidance for the sustainable utilization of industrial solid waste and the low-carbon development of soil stabilization materials.
Dust exposure levels were studied in a cement factory in Dar es Salaam, Tanzania, as part of an epidemiological study assessing chronic respiratory health effects. One hundred and twenty personal 'total' dust samples were collected from 80 randomly selected workers from eight a priori occupational groups (OGs) based on work areas using a 37 mm Millipore sampler. The between-group, within-group and within-worker variances were determined to assess the contrast in exposure level between the OGs and to estimate the attenuation and standard error of the theoretical exposure-response slope. Using mixed-effect model estimates, the probability of overexposure relative to the occupational exposure limit (OEL) was assessed for each OG. The geometric means of total dust exposure were higher in the cranes (38.64 mg m(-3)), packing (21.30 mg m(-3)) and crusher (13.48 mg m(-3)) than in the cement mill (3.23 mg m(-3)), kiln (2.87 mg m(-3)), raw mill (1.85 mg m(-3)), maintenance (1.16 mg m(-3)) and administration (0.29 mg m(-3)). The a priori grouping scheme seems to be an efficient scheme because of the high contrast in exposure level between the OGs (0.78) and minimal attenuation of the theoretical exposure-response slope (1.0%). When using the reduced mixed-effect model, the probabilities of overexposure () relative to the OEL of 10 mg m(-3) for total cement dust were higher in the crane (96%), packing (88%) and crusher (73%) than in the cement mill (16%), kiln (14%), raw mill (5%), maintenance (2%) and administration (0.01%).
From the late 1950s to the early 1970s elastic polysulphide sealants were used in outdoor seams between concrete blocks in prefabricated buildings. The sealants contained 5-30% polychlorinated biphenyls (PCBs). Due to the weathering of sealants in general and the replacement of seams with new PCB-free materials in the 1990s, PCBs have drifted to the soil adjacent to buildings. The objectives of this study were to survey PCB contamination in the surroundings of former PCB-containing buildings and to evaluate the risks to human health. Samples from soil, and also from blood serum of residents, were collected to obtain data for exposure assessment. The health risk assessment was based on deterministic and probabilistic calculations for cancer and non-cancer risks. Soil ingestion and dermal contact were considered the main routes of exposure and children the most important exposed group. The mean total PCB concentration was 6.83 mg/kg within 2m of the buildings and 0.52 mg/kg within 3-10 m from of the buildings. The deterministic risk assessment with conservative parameters resulted in lifetime cancer risk estimates on the order of 10(-6)-10(-7). The lifetime average daily dose (LADD) for PCBs was less than 10% of the reference dose (RfD) 0.02 microg/kg day, which is based on immunosupression in monkeys. The LADD corresponding to the total site attributable exposure was less than 10% of the estimated average dietary PCB intake in Finland. Children can, however, in worst cases be exposed to daily doses near the level of the RfD. Low cost measures are recommended to reduce possible exposure of children.