The most likely explanation for trouble with the hands coming into contact with fresh concrete is found in the ingredients of concrete or cement and the chemical reactions they possibly cause.
These effects can be a little bit delayed in time, like a few hours or the next day.
What is concrete?
Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is basically a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement. Concrete gets stronger as it gets older. 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.
One of the key ingredients in cement is lime, or Calcium oxide which may react to Calcium hydroxide, both substances or alkaline and caustic.
Occupational safety precaution say this:
Appendix D Lime Safety Precautions
Hydrated lime (calcium hydroxide), like most materials or chemicals in common use, is not dangerous to work with providing a few simple precautions are exercised. Quicklime (calcium oxide), also called “hot” lime, is considerably more dangerous to use than hydrated lime. While both types of lime are strongly alkaline, quicklime is much more caustic and can produce severe burns quickly when in contact with moist skin. It is also desirable to prevent as much hydrate as possible from coming into contact with workers’ skin. Usually danger from severe burns is remote, but prolonged contact of hydrated lime with a perspiring workers’ skin where the skin is also chafed by tight clothing has produced bad burns. Other persons with particularly sensitive skin have developed forms of skin irritation (dermatitis) through prolonged contact. There is no urgency in removing hydrated lime from skin, but it should be flushed off with water as soon as convenient. However, quicklime should be washed off or at least brushed off immediately after contact with skin, since it is caustic. Hot, humid weather conditions tend to heighten the caustic effect of hydrated lime on a worker’s skin.
Bathe or shower after a workday to cleanse the body entirely of lime and protective cream.
1. Skin burns--Wash thoroughly with soap and warm water to remove all lime. Apply a standard burn ointment used for heat or caustic burns, and cover with sterile bandages. Keep bandaged during healing to prevent infection.
2. Lime in the Eyes--Hold worker’s eye open and flush out with water immediately. Too much water cannot be used.
3. Report all burns from lime or cases of lime in eyes immediately so that medical attention can be provided without delay.
But these are not all the possible causes.
Construction Safety Association of Ontario: Cement Hazards and Controls Health Risks and Precautions in Using Portland Cement
Cement can cause ill health by skin contact, eye contact, or inhalation. Risk of injury depends on duration and level of exposure and individual sensitivity.
Hazardous materials in wet concrete and mortar include:
- alkaline compounds such as lime (calcium oxide) that are corrosive to human tissue
- trace amounts of crystalline silica which is abrasive to the skin and can damage lungs
- trace amounts of chromium that can cause allergic reactions.
- The hazards of wet cement are due to its caustic, abrasive, and drying properties.
Wet concrete contacting the skin for a short period and then thoroughly washed off causes little irritation. But continuous contact between skin and wet concrete allows alkaline compounds to penetrate and burn the skin.
When wet concrete or mortar is trapped against the skin—for instance, by falling inside a worker’s boots or gloves or by soaking through protective clothing—the result may be first, second, or third degree burns or skin ulcers. These injuries can take several months to heal and may involve hospitalization and skin grafts.
To protect skin from cement and cement mixtures, workers should wear:
- alkali-resistant gloves
- coveralls with long sleeves and full-length trousers (pull sleeves down - over gloves and tuck pants inside boots and duct-tape at the top to keep mortar and concrete out)
- waterproof boots high enough to prevent concrete from flowing in when workers must stand in fresh concrete
- suitable respiratory protective equipment such as a P, N or R 95 respirator when cement dust can’t be avoided
- suitable eye protection where mixing, pouring, or other activities may endanger eyes (minimum—safety glasses with sideshields or goggles, under extremely dusty conditions, tight-fitting unvented or indirectly vented goggles. Don’t wear contact lenses when handling cement or cement products).
When laying concrete block, have different sizes on hand to avoid cutting or hammering to make them fit.
- Work in ways that minimize the amount of cement dust released.
- Where possible, wet-cut rather than dry-cut masonry products.
- Mix dry cement in well-ventilated areas.
- Make sure to work upwind from dust sources.
- Where possible, use ready-mixed concrete instead of mixing on site.
- When kneeling on fresh concrete, use a dry board or waterproof kneepads to protect knees from water that can soak through fabric.
- Remove jewelry such as rings and watches because wet cement can collect under them.
- Clothing contaminated by wet cement should be quickly removed. Skin in contact with wet cement should be washed immediately with
large amounts of cool clean water.
- Don’t wash your hands with water from buckets used for cleaning tools.
- Provide adequate hygiene facilities on site for workers to wash hands and face at the end of a job and before eating, drinking, smoking, or using the toilet. Facilities for cleaning boots and changing clothes should also be available.
Skin contaminated with wet or dry cement should be washed with cold running water as soon as possible. Open sores or cuts should be thoroughly flushed and covered with suitable dressings. Get medical attention if discomfort persists. Contaminated eyes should be washed with cold tap water for at least 15 minutes before the affected person is taken to hospital.
The above is what makes nearly every form of cement problematic. A less generalised source of a multitude of problems is the variable nature of other ingredients:
Besides portland cement, concrete may contain other cementitious materials including fly ash, a waste byproduct from coal burning electric power plants; ground slag, a byproduct of iron and steel manufacturing; and silica fume, a waste byproduct from the manufacture of silicon or ferro-silicon metal. Some of these cementitious materials are similar to the volcanic ashes the Romans mixed with lime to obtain their cement binder.
Although these other ingredients should be chosen carefully by the manufacturer, the list of possible substances is quite long. Things like toxicity or allergenic potential are impossible to predict for that from general considerations. Some cement mixtures contain quite a lot of hexavalent chromium for example.
The most likely cause remains the alkaline nature of cement. Symptoms for the occupational safety hazard might look like:
These Problems Aren't Set in Stone
Concrete burns are a serious, sometimes disabling problem for exposed workers. Medical tests cannot predict who will get skin problems.
There are even cases of second hand cement exposure.
From all of this it should be clear to practice good occupational safety, to use protective gear and consult a medical practitioner as soon as any suspicious symptoms appear.
For a recent review of potentially problematic ingredients, see:
Rawaz Kurda & José D. Silvestre & Jorge de Brito: "Toxicity and environmental and economic performance of fly ash and recycled concrete aggregates use in concrete: A review", Heliyon, 4(4) 2018, DOI:10.1016/j.heliyon.2018.e00611
A study on the potential metal leaching and toxicity of FA, when used as binder in soil stabilization, showed significant differences in leaching characteristics with respect to heavy metals. […]
Numerous toxic elements show high enrichment in the fine particles of coal FA . In fact, the concentration of volatile elements, such as, Cd, Pb and Zn, increases with the decrease of FA particle size from coarse to fine [67, 68]. Moreover, the particles of FA have a large surface area in comparison to mass . The smaller particles have higher surface areas and contain significant surface concentrations of potentially toxic trace elements . According to Roy et al. , the leachability of elements (P, Fe, Al, B, K, and Ca) decreases for longer ages. The authors also sorted the relative concentrations of leached elements in 3 pH levels: (I) Alkaline: Se > B > Cr > Ni> Cu > Ba > As > Zn > Al; (II) Neutral: B > Cd > As > Se > Zn > Ni > Mn > Cu >Ba; and (III) Acidic: B ≫ Zn > Ca, F > Na > Mg, Co > Ni, Sr > Be > Cu, Pb, Al ≫ Si, Fe, K.
Based on a study by Theis and Gardner, the aqueous solubility of FA ranges is about 0.5–3% of total original mass. In spite of the insignificant total amount of leachate, the content needs to be precisely investigated and compared to the corresponding regulations.[…]
- It has been argued that FA concrete showed considerable leaching of heavy metals and must be regarded as hazardous materials while other studies show that heavy metal's concentrations in leachates from concrete containing FA are significantly lower and very close to the EPA drinking water standard limit;
- Long-term leaching from well-cured concrete produced with OPC and neither RCA nor NA release detectable concentrations of toxic metals;
- The leaching metals of FA decrease when they are incorporated in concrete. This reduction of the heavy metals' leaching between the FA powder and FA concrete may be related to the cement's ability to solubilize/stabilize the concentration of heavy metals due to chemical retention processes that allow the incorporation of the elements in the cement matrix, and physical retention by encapsulation. However, this study still suggests avoiding the use of FA concrete for drinking water tank and architectural concrete applications.
That means that concrete may contain quite a bit of problematic substances. Which substances anyone working with these cannot be predicted by just talking about "concrete". The actual mixture in use has to be analysed.