C.T.G. Maturity Meters  Provide Key to Tunnel Pour

Project:
Montreal-Laval Subway Expansion

Location:
Laval, Quebec, Canada

Owner:
Agence Metropolitaine de Transport Société de Transport de Montréal

Concrete Producer:
Unibeton Laval

Contractors:
Neilson Inc. Neilson-EBC s.e.n.c. Pomerleau

Architect/Designer:
Groupement S.G.T.M. (a consortium of engineering and architect firms)

Requirements:
Produce a flowable concrete that can be pumped over an 800 m length and be placed easily in the tunnel formwork.

Products:
CATEXOL A.E. 260
CATEXOL 1000 N
CATEXOL 1000 SP-MN
C.T.G. MTR 201 Maturity Meter

Situation:
Deliver more than 100,000 m3 (130,795 yd3) of concrete over a two-year period. The volume of each pour varied in size from 130 to 1,100 m3 (170 - 1,438 yd3). The concrete deliveries were made with no more than two trucks in the subway tunnel under the city.

Challenge:
The contractor requested a method for evaluating the in-place concrete strength development. The concrete had to reach 10 MPa (1,450 psi) before the contractor could remove the movable tunnel form. Timely removal of the forms permitted the project to stay on schedule and reduce costs associated with downtime.

Solution:
In order to achieve the requirements, nearly every cubic meter of concrete delivered to this project involved the use of  CATEXOL 1000 SP-MN.

AXIM Concrete Technologies, in cooperation with Unibeton Laval recommended evaluating the in-place strength with the CTG MTR 201 maturity meter. AXIM's Central Technical Group (CTG) developed its own maturity meter in the mid 1990s. The maturity meter  measures the real-time strength increase of the concrete in the form. Such information not only allows the contractor to safely remove forms when the minimum required strength is achieved, but also to optimize the production cycles in order to reduce overall cost. AXIM provided three maturity meters along with all the training on the technique and the use of the apparatus.

Highlights:
Each and every load of concrete exceeded the project requirements of flowability, strength etc. The contractor (Neilson Inc.) recognizes the value of the maturity technique and the support provided by AXIM and Unibeton to implement the technique for the project. Neilson typically stripped the concrete forms 12 hours after the end of the each placement versus waiting 24 to 36 hours for the concrete to attain the required strength. Neilson is so satisfied with the method that they continue to use it for other facets of the project (slabs, beams and walls) in order to accelerate form stripping and complete all concreting operations ahead of schedule.