Spray applications of fresh cementitious materials mix is regarded as beneficial for the repair of infrastructures such as bridges, culverts, underground structures, and other aged structures. Some advantages of wet process spray application over cast, hand-applied, and dry spray processes include reduction or elimination of formwork, faster and more efficient construction, and reduction of environmental problems associated with heavy dust. However, conventional sprayable cement has noted disadvantages, in particular, reduced ductility. In tension, only a very low percentage of strain can be tolerated before failure. Thus, such concrete is not suitable for applications where the concrete is expected to carry tensile loads, and even stresses caused by temperature changes can weaken the structure dramatically.
Researchers at the University of Michigan have developed a method of making sprayable fiber-reinforced cementitious composite to overcome shortcomings associated with wet process spray application. In particular, sprayable mortars have substantially improved tensile strain capacity with strain hardening behavior, improved flexural deformation capacity and improved tensile strength, compared with the respective properties of the other sprayable concrete or fiber reinforced concretes. The cement preferably comprises a hydraulic cement, such as Type I Portland cement, and calcium aluminate cement, with a predetermined range of weight ratio of water to cement. The discontinuous reinforcing fiber is preferably polyvinyl alcohol and the viscosity agent is preferably selected from cellulose-derived polymers and polyvinyl alcohol. This sprayed material substantially exhibits significant multiple cracking when stressed in tension with at least 1% tensile strain.
Applications and Advantages
- Repair of infrastructures and other applications requiring wet spray process application of cement
- Sprayable with enhanced pumpability and-nl-rebound property
- Improved tensile strain capacity with strain-nl-hardening behavior