ACI 506R-16 Guide to Shotcrete

ACI 506R-16 Guide to Shotcrete. 1.5—Preconstruction testing by contractor Preconstruction testing should be considered on large, complex jobs if previous data are not available, if proper- ties other than strength affect the design criteria, or if design requirements vary from one portion of the work to another. Before shotcrete construction starts, it is advised to conduct preconstruction testing. On relatively small jobs and where the materials, mixture proportions, equipment, fnish, and personnel have given satisfactory results on previous work, preconstruction testing may not be warranted. The purpose of preconstruction testing is to ensure the shotcrete work will achieve the following objectives: a) The shotcrete placement can properly encase the rein- forcement given the reinforcement design (size, spacing, and amount) b) The material meets the project specifcations c) The fnish will meet the owner’s expectations 1.5.1 Reinforcement―To determine if the reinforcement can be properly encased, shooting mockup panels that simu- late actual job conditions, such as reinforcing bar congestion, provides a suffciently reliable indication of the quality to be expected in the structure. The mockup panel should always be constructed with reinforcement similar to the most heavily reinforced section to be shot. The cut surfaces of the speci- mens should be carefully examined. Saw or core the panel when necessary to check the soundness and uniformity of the material. All cut and cored surfaces should be dense and mostly free from laminations, voids, and sand pockets. For evaluation of shotcrete, refer to ACI 506.4R and Fig. 1.5.1a and 1.5.1b. 1.6.2 Testing shotcrete: Quality control—QC normally includes mixture design review, shotcrete construction monitoring, and providing shotcrete samples. The default test for a typical shotcrete project is for the contractor to prepare shotcrete samples by shooting sample material panels (1.6.3), which are cored and tested for compressive strength. In addition, fexural strength tests may be required. When placing wet-mix shotcrete, the air content and temper- ature of the mixture (delivered material) should also be documented by the testing agency prior to placement when sample material panels are shot. The QC program should include the following: a) Shotcrete execution plan—The shotcrete contractor should prepare this plan. This should include shotcrete construction procedures and checklists (work method plan including shotcrete batching, mixing, supply, and placing procedures). The QC checklist should list critical features to be checked prior to placement, during placement, and after placement. A checklist should address surface preparation, reinforcement (size, location, and clearance),...