Specification for shotcrete mix design

After obtaining approval of his accelerator, other admixtures, cement, and aggregate from the Engineer, the contractor shall* submit his proposed shotcrete mix designs to the Engineer for initial evaluation and comment. Such designs shall include both regular shotcrete as well as a mix design for use as a finishing layer in areas receiving a waterproofing membrane. No sooner than 14 days after mix design submittal, the Contractor shall (afer giving the Engineer at least 48 hours prior notice) prepare test panels his proposed. Shotcrete mix design in the presence of the Engineer.

Selection Criteria for shotcrete mix designs

Mixture proportions (mix designs) for shotcrete shall be selected and approved on the basis of compressive strength tests of cores obtained from test panels fabricated in accordance with ASTM C1140 and the initial and final set properties of the mix as determined in accordance with ASTM* C403.

Test Panels

Test panels shall be at least 762mm by 762mm. Test panels shall be made* using equipment, water pressure, air pressure and nozzleman the Contractor proposes to use for the work. Four separated test panels shall be made, two shall be vertical placements (representing side placement of shotcrete) and two shall be overhead placements. From each panel, ten (10) cores shall be taken. Two (2) from each panel for testing at 8 hours after placement, two (2) from each panel for testing at 24 hours after placement, two (2) from each panel for testing at 3 days after placement, two (2) from each panel for testing at 7 days after placement and two (2) from each panel for testing at 3 days after placement. Cores shall be taken perpendicular to the test panel and cured in accordance with the requirements of ASTM C1140, until testing.

Mix design acceptance criteria

a. All cores shall meet or exceed the mix design strength requirements for 8 hours, 24 hours, 7 days and 28 days. The average compressive strength of all cores (for 8 hours, 24 hours, 7 days and 28 days) shall be 1.2 times the required minimum compressive strength specified.

b. Material from each sample panel shall meet or exceed the minimum initial and final set requirement.

Revision of approved mix design

Shotcrete mix designs, as approved by the Engineer, shall be based on the approvals for cement, admixtures and aggregates used with an approved mix. If the Contractor, for any reason, change his cement, any admixture and/or his aggregate source or gradation, the Contractor shall submit and obtain approval for any/all new mix constituents and provide a new mix design for approval by the Engineer.