Trials organized within a week from contact to find effective rock support for wet conditions
Contractor
Hochtief-Murphy JV
Processes
Sprayed ConcreteLocation
United Kingdom
Products
TamShot 80AFProject
During the construction of the Thames Crossing tunnel crossings, the contractor had experienced problems with insufficient early strength development of the shotcrete.
The main problem was the application of shotcrete on a very wet limestone surface where water was actively penetrating through many cracks.
Challenge
The contractor was unable to meet the original strength requirement of the Crossrail "modified J2" project with their original supplier and approach.
Hochtief-Murphy JV urgently called Normet to the site to help with the initial strength issues. A solution had to be found to safely and effectively support the rock in wet conditions. Normet had to act quickly to help the contractor get back on schedule.
Quick Facts
- Trials within a week to find a solution for the contractor’s urgent problem
- Valuable insight on improving early age strength development optimization
- Cemex DSM solution helped the contractor to get back on schedule
- Auditing procedures on-site to ensure an efficient process
Solution
The test runs took place the same week as the contact was made. Normet supplied the contractor with two different alkaline-free accelerators for trial use. Normet supplied the standard TamShot 80AF accelerator, which is supplied on most of Crossrail's SCL contracts, and the more powerful TamShot 100AF accelerator.
In discussions with the Hochtief-Murphy JV team, an additional outcome to ensure better performance was a switch to Cemex's dry silo mortar (DSM) solution, as Normet's additives and cement type in the silo are also optimised for early strength development, good opening times and ease of pumping.
Normet supported the contractor by auditing their procedures on site to ensure that all stages of the process from batching to injection were carried out efficiently. Normet provided recommendations to further optimise early strength development, such as better logistics options and the use of hot water and compressor air.
Normet Minimec, a small tunnel diameter injection robot, was used to inject the shotcrete.
Graph showing compressive strength vs concrete age
Project Outcome
Following successful trials with both set accelerators and the Cemex DSM solution, Hochtief-Murphy JV achieved very high early age strength development as shown in the chart. The construction of cross passages was conducted safely and effectively in the extremely wet ground conditions.
