You are here : Home > The Do-It-Yourself Corner > Advanced Tips

Advanced Tips Previous - 1 - 2 - 3 - 4 - 5 - 6

Factors affecting concrete resistance to scaling when exposed to freeze/thaw cycles in the presence of de-icing chemicalsFactors affecting concrete resistance to scaling when exposed to freeze/thaw cycles in the presence of de-icing chemicals

  • Water/cement ratio
  • Cement proportioning
  • Settlement
  • Air content and quality of air space network of hardened concrete
  • Quality of aggregates
  • Concreting:
  • Concrete placement.
  • Consolidation and finishing.
  • Curing
  • Structure maturity before first exposure to freeze/thaw cycles
  • Degree of saturation of the structure when applying de-icing chemicals
  • Severity of the environment in which the material has to function (freeze/thaw cycles, extreme temperature variations, temperature variation rate, salt concentrations, etc.)

To ensure long-term service ability of the structure, the municipality should demand documentation from the concrete supplier attesting that the materials delivered to the job site meet the minimum required characteristics.

The municipality must also require assurance from the contractor responsible for the concreting work that the product used will perform well.

In return, the municipality must provide contractors with an adequate soil analysis. This can avoid additional costs due to unforeseen occurrences and allow contractors to be better able to guarantee the work done and to do it in the timeframes set out in the schedule.

If the municipality requires a delivery date for the work accompanied by a penalty clause for any possible delays, then it should also offer a bonus system to encourage early delivery.

Although the municipality must generally award work to the lowest bidder, insofar as possible, it should favour the contractor who offers the best guarantee for long term performance.

There are tests specifically designed to assess the quality of the concrete of existing concrete structures (freeze-thaw resistance, scaling and compressive strength resistance, etc.).

The following table sums up in a few lines the main requirements a municipality might formulate for high-performance concrete.

SIDEWALK CONCRETE
(plastic concrete of normal density)
Minimum requirements for durable concrete exposed to de-icing chemicals 28 day compressive strength (f'c 28d): 32 MPa min.
Fresh concrete
Recommended cementing material content:
Volume of large aggregates (5-20 mm):
Cement/water ratio:
Settlement:
Air content: 		407 kg/m3 (130 L/m3)
393 L/m3
0,43 max.
90 mm max. *
5,8% min.
. Optimal characteristics of the air space network (CSA A23.2-17C)
Air space mean spacing factor, (L):
Air space volume percentage:
Air space volume surface: 		+- 150 um
+- 6 %
+- 30 mm2/mm3 min.
. * This value must not exceed 40 mm when using slip formwork.
Scaling resistance of exposed concrete surface (ASTM C-672)
Scaling Class
1
2
3 		Scaling
0 à 400 g/m2
400 à 800 g/m2
800 à 1200 g/m2 		Scaling Resistance
High
Moderate
Poor
Resistance to rapid freeze-thaw cycles (ASTM C-666, procedure A, 300 cycles)
Durability Class
1
2
3 		Value of Durability Factor
90 % à 100 %
80 % à 90 %
60 % à 80 % 		Freeze-Thaw Cycle Resistance
High
Moderate
Poor
* This value must not exceed 40 mm when using slip formwork.

As shown in this table, certain requirements are intended for the manufacturer whereas others apply to the contractor responsible for the concreting. Municipalities may require a certain class of scaling and durability in regard to the degree of exposure of structures and desired performances.

Previous - 1 - 2 - 3 - 4 - 5 - 6

© 2006 BétonMobile.com  |  Web Design by GENERATION-CLIK