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HAZARDS OF CONCRETE EXPOSURE. What is the difference between cement & concrete?. Cement is an ingredient in concrete. Concrete is a mixture of aggregates (sand, gravel or crushed stone) and paste (water & portland cement)
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What is the difference between cement & concrete? • Cement is an ingredient in concrete. • Concrete is a mixture of aggregates (sand, gravel or crushed stone) and paste (water & portland cement) • Portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete, just as stainless is a type of steel and sterling a type of silver. • Cement comprises from 10 to 15 percent of the concrete mix, by volume. Through a process called hydration, the cement and water harden and bind the aggregates into a rocklike mass. This hardening process continues for years meaning that concrete gets stronger as it gets older.
How is portland cement made? • Ingredients such as limestone, marl, shale, iron ore, clay, and fly ash are crushed and screened and placed in a rotating cement kiln. • The kiln is a large horizontal pipe with a diameter of 10 to 15 feet and a length of 300 feet or more. One end is raised slightly. The raw mix is placed in the high end and as the kiln rotates the materials move slowly toward the lower end. Flame jets are at the lower end and all the materials in the kiln are heated to high temperatures that range between 2700 and 3000 Fahrenheit . This high heat changes the raw materials and forms new compounds.
How is portland cement made? • For each ton of material that goes into the feed end of the kiln, two thirds of a ton the comes out the discharge end, called clinker. This clinker is in the form of marble sized pellets. The clinker is very finely ground to produce portland cement. A small amount of gypsum is added during the grinding process to control the cement's set or rate of hardening.
What are the hazards of concrete exposure? • Hazardous Materials in Cement: • Alkaline Compounds such as lime (calcium oxide) • Corrosive to human tissue • Trace amounts of crystalline silica • Abrasive to skin and can cause lung damage • Trace amounts of chromium • Can cause allergic reactions
What are the health effects of concrete exposure? • Health Effects: • Contact Dermatitis (Skin) – 4 Types • Dryness Irritation • Allergic Reaction • Chronic – low exposure of a long period • Acute – high exposure of a short period • 2. Inhalation (Lungs)
Contact Dermatitis – Dryness Irritation • Dryness Irritation • By nature cement will pull and retain moisture. • Anyone that comes in contact with concrete will experience skin dryness. • This condition normally subsides after thorough washing and moisturizing.
Contact Dermatitis – Allergic Reaction • Allergic Reaction: • Caused by the individuals sensitivity to hexavalent chromium. A small but significant percentage of people will develop and allergy to chromium. • The cumulative effect of daily exposure may take months or years to cause a reaction. • Individuals may develop both skin and respiratory allergies. Respiratory allergy is called occupational asthma and it’s symptoms include wheezing and difficulty breathing • Chrome sensitization is irreversible and sensitized individuals must avoid contact with cement, wet or dry. • Symptoms appear much like chronic dermititis, with swelling, redness, oozing, cracking, stinging, blisters and scaling.
Contact Dermatitis – Chronic • Chronic – low exposure of a long period • Found in 80% of Concrete Workers • Caused by daily exposure to small amounts. • Symptoms include stinging, itching, redness, swelling, cracking, blisters, scaling, fissures and bleeding. • Wounds heal very slowly and infections are likely.
Contact Dermatitis – Acute • Acute (Cement Burns) – high exposure of a short period • Occur within minutes or hours of continuous exposure. • Accelerates when clothing, boots or gloves are saturated with wet concrete and are rubbing against the skin. • Important to note that unlike acids which cause a burning sensation very quickly, Alkali does not. Alkali causes no heat or pain until it is too late to wash off. • By the time pain is felt, the alkalis have soaked into the skin. Many cement burn victims require skin grafts leaving massive scars.
Inhalation of Concrete Dust • Exposure occurs when emptying bags, sanding, grinding or cutting. • Short term exposure irritates the nose and throat and causes choking and difficult breathing. • Prolonged or repeat exposure can lead to a disabling and often fatal disease called silicosis. • Some studies indicate a link between crystalline silica exposure and lung cancer.
Controls – Personal Protective Equipment • To Protect Skin and Lungs: • Alkali resistant, at least mid length gloves. Avoid gloves with a cotton back. • Rubber boots high enough to prevent concrete from flowing in. • Long sleeved shirt and full length pants tucked into boots with duct-taped to keep concrete from getting in. • If kneeling on fresh concrete use water proof knee pads or wood board. • When dust can’t be controlled using water a suitable respirator must be worn. • Eye protection when mixing, pouring. Safety glasses with side shields and goggles in extreme dusty conditions. Avoid wearing contact lenses in dusty conditions.
Controls – Work Practices • Work in ways that minimize dust. When possible, wet cut rather than dry cut. • Mix dry cement in well ventilated areas. Pour so dust in minimized. Keep head out of dust plume. • Work up wind of dust sources. • Remove jewelry such as rings and watches because wet concrete can collect under them.
Controls – Hygiene • Clothing contaminated by wet concrete should be quickly removed. Skin in contact should be washed immediately with cool clean water. • Don’t wash your hands or exposed skin with water from buckets used for cleaning tools.
