Hard troweling is a process by which a finisher uses a steel trowel to densify the surface of the concrete. This finish is optional and produces a hard, smooth surface. Hard troweling is not recommended for air-entrained concrete for several reasons. Read more on finishing air-entrained concrete. Hot Weather Concreting
Air-entraining admixtures facilitate the development of a stable air-void system within concrete that increases the durability of the concrete. These admixtures impart air entrainment that results in: Increased resistance to deterioration from cyclic freezing and thawing Improved workability and cohesiveness of concrete placement
The optional requirements checklist of ACI 301 4 states that intentionally entrained air should not be incorporated in normal weight concrete slabs that require a dense, polished,...
Air-entrainment delays the timing when bleed water may eventually come to the surface of the concrete. In general, air-entrainment reduces the amount of bleed water coming to the surface after concrete placement. Finally, air-entrained concrete has a tendency to blister when applying a tight, steel & trowel finish to the surface of the slab.
Air-entrained concrete should not be used for interior floor slabs with a hard troweled surface that are not subjected to freeze-thaw cycles or deicing salt application. If entrained air is required to protect inner slabs from freezing and thawing cycles, air levels greater than 3% should be avoided. Concrete Delamination Repair
There is a chance of blistering and/or delaminations when you hard trowel air entrained concrete. See ACI 302.1R 5.7.1. I would recommend keeping the air and either eliminating the trowel finish or minimize your water content (slump) and delay the troweling until all the bleed water is gone and don't over trowel. newtron (Computer) (OP)
19 votes, 20 comments. For durability reasons, I need to specify my concrete to meet certain chloride resistance requirements, and in the standard …
Concrete shall be used and placed in final position within 1 hour after initial mixing or discarded at that time. Allow the concrete to reach initial set, wait for all water to evaporate from the surface before finishing with a trowel or broom.
Entrained air in concrete reduces the rate of bleeding and promotes early finishing that will produce a dense, impermeable surface layer. A cool subgrade delays set in the bottom relative to the top layer. Delaminations are more likely to form if: The underlying concrete sets slowly because of a cool subgrade.
Air-Entrained Concrete Home > Cement and Concrete > Working with Concrete > Air-Entrained Concrete Air-entrained Concrete Air-entrained concrete contains billions of microscopic air cells per cubic foot. These air pockets relieve internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes.
Air Entrainment During mixing, all concrete will trap some air in the form of big bubbles. Those big bubbles aren't good — we vibrate the concrete to get rid of them. But the tiny, well-spaced bubbles we call entrained air are desirable, especially in concrete that will be exposed to freezing weather, such as sidewalks, driveways, and garage slabs.
voids left by the screed. Hard steel trowel finish is not recommended for air-entrained concrete. 3. Concrete shall be used and placed in final position within 1 hour after initial mixing or discarded at that time. 4. Allow the concrete to reach initial set, wait for all water to evaporate from the surface before finishing with a trowel or ...
Statement #1, "Hard Trowel Finish on Air-Entrained Concrete," published in Concrete International in January 2003, detailed that organization's support for this recommendation. Design professionals may assume that measurement of air content is not necessary for non-air-entrained con-crete. That assumption, however, is not true.
Top-down setting occurs when bases and subgrades are colder than air temperatures so the concrete along the base sets slower than concrete along the top surface. The more plastic and slower...
Alternatively, use a hand trowel but kneel on wooden boards when you need to be on the slab to prevent leaving deep impressions. 3 Try a broom finish. Most people end with a broom finish to create a non-slip surface. You can do this with or without a preceding trowel finish. Use a medium stiff or stiffer shop broom (the wide rectangular kind).
The concrete has entrained air or the air content is higher than desirable for the application. The concrete mixture is sticky from higher cementitious material or sand-fines content. Environmental conditions during placement are conducive to rapid drying causing the surface to "crust" and appear ready to finish.
Do not hard-trowel air-entrained concrete. 5. Specify a minimum cementitious material content in relation to the maximum aggregate size as shown in Table 1, to ensure good finishability of the fresh concrete and good durability of the hardened concrete. 6. Do not use high-slump concrete. Control water additions at the truck.
Sorry guys, but we use steel trowel finishing on air entrained concrete routinely. Part of the success with that in our area is the type of coarse aggregate we typically use. It doesn't "bleed" as much as less porous aggregates, thus there is less potential to trap the bleed water under the trowel-densified surface, which causes blistering.
It is not recommended to slick-finish air-entrained concrete. A slick finish is achieved by repeatedly passing a steel trowel over the surface, like a basement slab, garage slab, or warehouse floor. Finishers can finish a surface to a mirror-like sheen. The process of slick finishing can be detrimental to air-entrained mixes for two reasons.
Hard troweled finishes are typically only applied to non-air interior concrete mixes. The presence of air can cause delamination and blistering during the lifespan of the concrete. The Pea Gravel Concrete Finish: Pea gravel concrete finishes require a completely different mix design which typically consists of 50% sand and 50% pea gravel.
"Adding air entrainment in the range of 6% to 7.5% (and sometimes higher) is needed in order to meet specified weights." So the adage that you shouldn't use a power trowel on air-entrained concrete doesn't apply in the case of lightweight concrete; you can use a power trowel, but only with proper timing.
Can an air-entrained concrete slab be given a hard-troweled finish? Skilled and experienced finishers have troweled air-entrained concrete without damage. However, the ACI Flatwork Finisher Certification program does not recommend troweling air-entrained concrete, as the formation of blisters and delaminations can occur even when troweled by the...
4. Use correct timing for all finishing operations and avoid the use of steel trowels for exterior concrete slabs. 5. Specify air-entrained concrete. In cold weather, concrete temperature should be at least 50°F [10°C], contain an accelerating admixture, and be placed at a lower slump.
Broom finishes are typically applied to exterior (air entrained) concrete that will be exposed to weather. The Hard Trowel Finish: The hard trowel finish can likely be found in the garage of your own home as well as the floors of large commercial buildings such as Wal-Mart or Costco. This finish takes longer to achieve than the broom finish due ...
When water-reducing admixtures and waterproofing admixtures are used in concrete to receive a hard-troweled finish, ASCC concrete contractors have noted air contents exceeding 3%. In many cases, the contractors are not alerted to this issue because air content is not reported in the concrete mixture design submittal or measured during placement.
ACI 302.1R-96, "Guide for Concrete Floor and Slab Construction," states that entrained air is not recom-mended for concrete to be given a smooth, dense, hard-troweled finish. ASCC concrete contractors will hard-trowel air-entrained concrete if required by specification, but only with the acknowledgment that the risk associ-
entrained concrete). A core sample of air-entrained concrete with a machine trowel finish exhibited the fol-lowing: • Percentage of air in the top 4mm of slab surface: 0% • Depth at which the air content is incorrect: up to 25 mm • Depth at which the air bubble spacing is incorrect: up to 85 mm Considerations: In saturated freeze-thaw ...
Troweled Finish Trowel finish is the most common and popular finish of concrete used for major types of applications. After the concrete is laid in the formwork and leveled, the trowel is used to smooth and fine-level the surface of concrete. Fig 1: Trowel Finished Concrete. Trowels are available in both manual and mechanical types.
6. TROWEL the concrete when required for its end use. For sidewalks, patios, driveways and other exterior ap-plications, troweling is not usually required. Air entrained concrete should not be troweled. If trowel finishing of air-entrained concrete is required by specifications, ex-treme caution should be exercised when timing the fin-ishing ...
Air-entrained structural lightweight concrete can be successfully incorporated in construction of sus-pended floor slabs, and has a long history of successful use. Structural and fire rating considerationsrequire that the air entrainment be maintained in the structural lightweight concrete. It can be finishedwith modern finishing equipment and t...
