Cold weather working - Five Star Repair Concrete

This application guide contains important information on the installation and application, of the concrete repair products listed. It includes information on the desirable weather conditions for application, storage, protection and curing advice for the system. Please note it is the responsibility of the installing contractor to form the project specific Method Statement that defines the appropriate Schedule of Works to reflect the project criteria. If any operations do not seem applicable, or if a required operation is not included, clarification should be sort from the Design Engineers or Weber.

Five Star Repair Concrete is a pre-blended cementitious repair concrete which complies with the Highways Agency Specification for Highway Works white book Series 1700 Structural Concrete and Department of Transport specification BD 27/86 for a high strength flowing concrete. Conformity testing to BS EN 1504-3 has confirmed that Five Star Repair Concrete meets the requirements for a Class R4 repair product.

Five Star Repair Concrete is a cement-based product and many of the considerations and restrictions applying to the use of cement or concrete in cold weather apply also to Five Star Repair Concrete. The colder it becomes the longer it takes for concrete to harden and if the setting concrete is frozen, damage will result. It is generally recommended that during cold weather the temperature of the concrete mix as placed should never be less than 5°C (41°F) and that the placed material should be maintained at as high a temperature as practical, but in any case exceeding 5°C (41°F). Similarly, it is advised that concreting be stopped when the air temperatures reaches about 5°C (41°F) on a falling thermometer. Such concreting restrictions apply to Five Star Repair Concrete.

During winter, Five Star Repair Concrete will have a low temperature, having been prepared from cold materials; heat losses from shutter, cold reinforcing bars or when poured between larger material masses will also reduce the heat development of the setting cement. In many cases the substrate may have a temperature below that of the Five Star and thus act as a heat sink causing further heat loss.

Materials storage

The bags of concrete should be stored in a warm dry environment, off the ground. Temperature of storage plays a major role in keeping the materials from freezing in cold weather. It is a common fallacy to mix cement and aggregates with warm water and expect the concrete mix to warm up in the process. Work carried out by the C&CA many years ago and repeated by Weber using Five Star Repair Concrete as the test product showed clearly that it is the powder that governs the temperature of the mixed material, not the water. The heat capacity of the powder and its relatively larger volume compared to that of water is the governing factor.

Substrates

On no account should the Five Star Repair Concrete be placed on frozen concrete or adjacent to cold steel. Provide heating to raise the temperature of the substrate concrete, steel etc to above 5°C, preferably 10°C for 24 hours prior to application. The use of tenting and heating is an accepted process in many cold countries in order to keep contracts running even in winter.

Mixing 

We recommend mixing the product for at least 3 minutes to ensure full dissolution of components and good dispersion and a water content of 3.1 to 3.3L per 25kg bag and no more than 3.3 litres maximum for a flowable mix. A pumpable mix needs about 3.1L water per 25kg bag, but this depends on site temperature and the equipment used. It would be helpful if hot water is used as it will tend to raise the temperature of the mixing equipment slightly. For mixing large volumes of Five Star Repair Concrete, we would recommend the use of a mixer pump such as a Putzmeister P13, which is a twin piston pump. Worm-drive pumps are not as good as they tend to get worn down by the sharp aggregates in the concrete.

Protection from frost

Maintain temperature during application 

It has already been stated that concreting should not continue when air temperatures reach 5°C on a falling thermometer. When leaving concreted areas overnight in winter it is safest to assume that frost will occur and take the necessary precautions. Leave the shuttering in place as long as possible and cover any exposed concrete with strawboard, expanded polystyrene or similar insulating material. Wrap the whole area in dry sacking and, if possible, keep enclosed areas gently heated to a temperature not exceeding 25°C. Heaters are available that exhaust to the outside of an enclosure or building and just blow in warm air. That eliminates the carbonation problem. When using hot, dry air in an enclosure, the concrete surface can dry out quickly, leading to crusting or plastic shrinkage cracking. Adequate ventilation should be provided for the workforce.

Maintain temperature during curing 

Temperatures must be maintained above 5°C for at least 24 hours if not 48 hours. This depends on the ambient temperature. The continued use of the tenting and heating system is a common practice but the use of insulated blankets or heated blankets is better recommended as this method does not dry out the concrete surface and lead to plastic shrinkage.

Five Star Repair Concrete is based on rapid hardening cement and, as such, will mature more rapidly than materials mixed on site with ordinary Portland cement. In order to study the rate of development of strength at various temperatures 100m cubes of Weber Five Star Repair Concrete were made using 3.3 litres of water per 25kg of dry mix. Compressive strength was determined at various periods of time and the results plotted to produce the graphs below. 

The graph may be used as a guide to predict strength. Values for intermediate temperatures may be estimated by inspections or an alternative method such as the Sadgrove method may be used. This uses the principle that since cement hydrates more slowly at lower temperatures its strength is equivalent to that of similar material at a shorter time duration. Five Star Repair Concrete that has attained a strength of 10 N/mm2 is normally considered to be sufficiently mature to withstand further damage from frost.

Contact us

If you have any questions or would like assistance, please contact our technical team:

Our technical team is available Monday to Friday, 8:30am until 5.00pm.

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