Concrete and Masonry Work

1. Concrete and Masonry Work • Different forms of concrete work • Each has it’s own unique hazards • Lift Slab • Pre-stressed Concrete • Concrete Pumping • Masonry wall construction • Cast in Place • 1926 Subpart Q – Concrete and Masonry Construction

2. General Requirements for Concrete Work • 1926.701: Construction loads. No construction loads shall be placed on a concrete structure unless the employer determines, based on information received from a person who is qualified in structural design, the structure is capable of supporting the loads.

3. Rebar Hazards • 29 CFR 1926.701(b), Reinforcing steel. All protruding reinforcing steel, onto and into which employees could fall, shall be guarded to eliminate the hazard of impalement.

4. Mushroom Style Rebar Caps • A January 15, 1997, memo addressing the small mushroom style plastic rebar caps, commonly used in construction, was issued to provide information on studies conducted by the California Division of Occupational Safety and Health (Cal/OSHA) showing the general ineffectiveness of rebar caps as impalement protection under requirements in 29 CFR 1926.701(b).

5. Wire Mesh Hazards • Employers shall take measures to prevent unrolled wire mesh from recoiling. • Measures may include, but are not limited to, securing each end of the roll or turning over the roll.

6. Bull Floats • 29 CFR 1926.702(h) • Bull float handles used where they might contact energized electrical conductors, shall be constructed of nonconductive material or insulated.

7. Post-tensioned Concrete • Concrete is strong in compression and weak in tension. • Designers use post-tensioning as a way to reinforce concrete by prestressing it. • Post-tensioning is a method of prestressing in which the tendons are tensioned after the concrete has hardened and the prestressing force is primarily transferred to the concrete through the end anchorages. • Post-tensioning can help create concrete components that are thinner, longer, and stronger than before.

8. Post-tensioning Operations • The hazards with post-tensioning involve the jacks and cables used to tension the concrete. • Keep unnecessaryemployees (except those essential to the post-tensioning operations) away from behind the jack during tensioning operations.

9. Concrete Buckets • Do not allow employees under concrete buckets

10. Concrete Pumping Systems • Compressed air hoses used on concrete pumping system shall be provided with positive fail-safe joint connectors to prevent separation of sections when pressurized. • No employee shall be permitted to apply a cement, sand, and water mixture through a pneumatic hose unless the employee is wearing protective head and face equipment.

11. Cast In Place Concrete • With cast in place construction, the concrete is poured and cures on site. • This type of work requires the use of forms and shoring to serve as the “mold” for the concrete.

12. Formwork • 29 CFR 1926.703 • Formwork shall be designed, fabricated, erected, supported, braced and maintained so that it will be capable of supporting without failure • Drawings or plans, including all revisions, for the jack layout, formwork,, working decks, and scaffolds, shall be available at the jobsite. • Forms cannot be removed unless it has been determined the concrete has gained sufficient strength to support the loads. • All Shoring equipment (including equipment used in reshoring operations) shall be inspected prior to erection to determine that the equipment meets the requirements specified in the formwork drawings.

13. Vertical Slip Form

14. Precast Concrete • Precast concrete consists of concrete (a mixture of cement, water, aggregates and admixtures) that is cast into a specific shape at a location other than its in-service position. • The concrete is placed into a form, typically wood or steel, and cured before being stripped from the form, usually the following day. • These components are then transported to the construction site for erection into place.

15. Precast Concrete • 29 CFR 1926.704 • Precast concrete wall units, structural framing, and tilt-up wall panels shall be adequately supported to prevent overturning and to prevent collapse until permanent connections are completed. • Lifting hardware shall be capable of supporting at least five times the maximum intended load applied transmitted to the lifting hardware. • No employee shall be permitted under precast concrete members being lifted or tilted into position except those employees required for the erection of those members.

16. Tilt-Up Concrete Construction • In tilt-up concrete construction, the walls are poured on-site in horizontal molds. • After they have cured, the walls are tilted up into place and secured. • Panels are cast as near to the final position as possible.

17. Lift-Slab Construction • The method entails casting floor and roof slabs on or at ground level and jacking them up into position. • Special lifting collars are provided in the slabs at columns. • Bond breaking compounds are applied between slabs to separate them. • After the slabs have cured long enough to reach a prescribed strength, powerful hydraulic jacks mounted on top of the columns lift the slabs into their respective positions.

18. Lift-Slab Operation

19. Lift-Slab Operations • 29 CFR 1926.705 • Lift-slab operations shall be designed and planned by a registered professional engineer who has experience in lift-slab construction. • Jacks/lifting units shall not be loaded beyond their rated capacity as established by the manufacturer. • Jacking operations shall be synchronized in such a manner to ensure even and uniform lifting of the slab. • Under no circumstances, shall any employee who is not essential to the jacking operation be permitted immediately beneath a slab while it is being lifted.

20. Masonry Construction • Masonry construction involved building structures from individual units laid in and bound together by mortar. • Includes use of bricks, concrete blocks, stone, etc.

21. Masonry Construction • 29 CFR 1926.706 • Limited Access Zones • Shall be established whenever a masonry wall is being constructed. The limited access zone shall conform to the following: • Be established prior to the start of construction of the wall. • Be equal to the height of the wall to reconstructed plus four feet, and shall run the entire length of the wall. • Be established on the side of the wall which will be unscaffolded. • Be restricted to entry by employees actively engaged in constructing the wall. No other employees shall be permitted to enter the zone. • Remain in place until the wall is adequately supported to prevent overturning and to prevent collapse. • If the height of wall is over eight feet, the limited access zone shall remain in place until permanent supporting elements of the structure are in place.

22. Limited Access Zone

23. Masonry Construction • Walls Over 8 Feet in Height • All masonry walls over eight feet in height shall be adequately braced to prevent overturning and to prevent collapse unless the wall is adequately supported so that it will not overturn or collapse.