Placing and Finishing Concrete - Design and Control of Concrete Mixtures - page 211

Protect Your Back. All materials used to make concrete—
portland cement, sand, coarse aggregate, and water—can
be quite heavy, even in small quantities. When lifting
heavy materials, the back should be straight, legs bent,
and the weight between the legs as close to the body as
possible. Mechanical equipment should be used to place
concrete as close as possible to its final position. After the
concrete is deposited in the desired area by chute, pump,
or wheelbarrow, it should be pushed—not lifted—into
final position with a shovel; a short-handled, square-end
shovel is an effective tool for spreading concrete, but spe-
cial concrete rakes or come-alongs also can be used.
Excessive horizontal movement of the concrete should be
avoided; it not only requires extra effort, but may also lead
to segregation of the concrete ingredients.
Protect Your Skin. When working with fresh concrete,
care should be taken to avoid skin irritation or chemical
burns (see warning statement in the box). Prolonged con-
tact between fresh concrete and skin surfaces, eyes, and
clothing may result in burns that are quite severe,
including third-degree burns. Eyes and skin that come in
contact with fresh concrete should be flushed thoroughly
with clean water. If irritation persists, consult a physician.
For deep burns or large affected skin areas, seek medical
attention immediately.
The A-B-Cs of fresh concrete's effect on skin are:
Abrasive Sand contained in fresh concrete is abrasive
to bare skin.
Basic & Portland cement is alkaline in nature, so wet
Caustic concrete and other cement mixtures are
strongly basic (pH of 12 to 13). Strong bases
—like strong acids—are harmful, or caustic
to skin.
Drying Portland cement is hygroscopic—it absorbs
water. In fact, portland cement needs water
to harden. It will draw water away from any
material it contacts—including skin.
Clothing worn as protection from fresh concrete
should not be allowed to become saturated with moisture
from fresh concrete because saturated clothing can
transmit alkaline or hygroscopic effects to the skin.
Clothing that becomes saturated from contact with fresh
concrete should be rinsed out promptly with clear water
to prevent continued contact with skin surfaces.
Waterproof gloves, a long-sleeved shirt, and long pants
should be worn. If you must stand in fresh concrete while
it is being placed, screeded, or floated, wear rubber boots
high enough to prevent concrete from getting into them
( PCA 1998 ).

WARNING: Contact with wet (unhardened) concrete,
mortar, cement, or cement mixtures can cause SKIN IRRI-
TATION, SEVERE CHEMICAL BURNS (THIRD-
DEGREE), or SERIOUS EYE DAMAGE. Frequent
exposure may be associated with irritant and/or allergic
contact dermatitis. Wear waterproof gloves, a long-
sleeved shirt, full-length trousers, and proper eye protec-
tion when working with these materials. If you have to
stand in wet concrete, use waterproof boots that are high
enough to keep concrete from flowing into them. Wash
wet concrete, mortar, cement, or cement mixtures from
your skin immediately. Flush eyes with clean water
immediately after contact. Indirect contact through
clothing can be as serious as direct contact, so promptly
rinse out wet concrete, mortar, cement, or cement mix-
tures from clothing. Seek immediate medical attention if
you have persistent or severe discomfort.

REFERENCES

ACI Committee 207, Roller Compacted Mass Concrete, ACI
207.5R-99, American Concrete Institute, Farmington Hills,
Michigan, 1999, 47 pages.

ACI Committee 301, Specifications for Structural Concrete,
ACI 301-99, American Concrete Institute, Farmington
Hills, Michigan, 1999, 49 pages.

ACI Committee 302, Guide for Concrete Floor and Slab
Construction, ACI 302.1R-96, American Concrete Institute,
Farmington Hills, Michigan, 1996, 65 pages.

ACI Committee 304, Guide for Measuring, Mixing,
Transporting and Placing Concrete, ACI 304R-00, American
Concrete Institute, Farmington Hills, Michigan, 2000, 41
pages.

ACI Committee 309, Guide for Consolidation of Concrete,
ACI 309R-96, American Concrete Institute, Farmington
Hills, Michigan, 1996, 39 pages.

ACI Committee 347, Guide to Formwork for Concrete, ACI
347R-94, reapproved 1999, American Concrete Institute,
Farmington Hills, Michigan, 1999, 34 pages.

ACI, “Vapor Retarder Location,” Concrete International,
American Concrete Institute, Farmington Hills, Michigan,
April 2001, pages 72 and 73.

Colley, B. E., and Humphrey, H. A., Aggregate Interlock at
Joints in Concrete Pavements, Development Department
Bulletin DX124 , Portland Cement Association, http://
www.portcement.org/pdf_files/DX124.pdf , 1967.

Concrete Manual, 8th ed., U.S. Bureau of Reclamation,
Denver, revised 1981.