ThormaJoint – the proven bridge expansion joint
The first choice for bridge engineers seeking effectiveness, economy and reliability
ThormaJoint is a combination of an elastomer modified binder, BJ200 and a carefully selected aggregate, BJ Stone. The joint is constructed in-situ and is a hot process.
BJ200 is a special blend of bitumen, polymers, fillers and a surface active agent, formulated to combine good fluidity at process temperatures with low temperature flexibility and ambient temperature slump control. It is delivered to site in bags in its solid state, where it is heated in a special pre-heater to its normal application temperature in accordance with the manufacturer’s recommendations.
BJ200 is available in a range of grades and is selected according to the climate in which the joint is to be installed. This ensures that it remains flexible even in very cold conditions but does not become too soft in very warm conditions (table 1). BJ Stone is a single-size aggregate preferably from the Basalt, Gritstone, Gabbro or Granite groups. For the standard joint the aggregate size is 20mm to BS63. In special cases other sizes may be specified, e.g. a 14mm size in shallow joints. The use of a single-size aggregate enables a high binder content to be reached and ensures a constant ratio of stone to BJ200, important to give the optimum combination of flexibility and load bearing capacity.
The stone is cleaned, sized and bagged for despatch to site. Immediately prior to use it is further cleaned by being rotated in a perforated drum mixed whilst being heated by hot compressed air (HCA) to a working temperature range of 150°C-190°C. All joints extend the full depth of the asphalt road surfacing and waterproof membrane down to the deck concrete. In certain instances the engineer may decide that a rebate may be created in the concrete, to increase the depth of the joint to the required dimension (table 1).
In gaps up to 30mm wide, an aluminium flashing strip spans the gap to prevent stone entering the gap during joint construction or under the punching action of subsequent traffic. For gaps over 30mm wide, a steel plate is used which also serves to distribute wheel loads across the gap (table 2).
The joint develops a very strong bond to the concrete and to the vertical faces of the adjacent asphalt.
