Section 1908A — California Building Code (Title 24, Part 2)

SHOTCRETE

1908 A .1 General. Shotcrete is mortar or concrete that is pneumatically projected at high velocity onto a surface. Except as specified in this section, shotcrete shall conform to the requirements of this chapter for reinforced concrete and the provisions of ACI 506R. The specified compressive strength of shotcrete shall not be less than 4,000 psi (27.6 MPa) .

[DSA-SS] Exception: The reference to ACI 506R shall be to ACI 506.2, unless otherwise approved by the enforcing agent.

Concrete or masonry to receive shotcrete shall have the entire surface thoroughly cleaned and roughened by a mechanical method acceptable to the enforcement agency, and just prior to receiving shotcrete shall be thoroughly cleaned of all debris, dirt and dust. Concrete and masonry shall be wetted before shotcrete is deposited, but not so wet as to overcome suction.

1908 A .2 Proportions and materials. Shotcrete proportions shall be selected that allow suitable placement procedures

where d b is the diameter of the largest reinforcement in the topping slab.

1905A.1.13 ACI 318, Table 21.2.2. Replace Table 21.2.2 as follows:

TABLE 21.2.2

STRENGTH REDUCTION FACTOR φ FOR MOMENT, AXIAL FORCE, OR COMBINED MOMENT AND AXIAL FORCE


NET TENSILE STRAINεt	CLASSIFICATION	φ	φ	φ	φ
NET TENSILE STRAINεt	CLASSIFICATION	Type of transverse reinforcement	Type of transverse reinforcement	Type of transverse reinforcement	Type of transverse reinforcement
NET TENSILE STRAINεt	CLASSIFICATION	Spirals conforming to 25.7.3	Spirals conforming to 25.7.3	Other	Other
εt ≤ εty	Compression- controlled	0.75	(a)	0.65	(b)
εty <εt < 0.005	Transition1,2	0.75 0.15 ε_t_ ε_ty_ – ε_t_ ε_ty_ – ----------------- + *	(c)	0.65 0.25 ε_t_ ε_ty_ – ε_t_ ε_ty_ – ----------------- + *	(d)
εt ≥ 0.005	Tension- controlled_3_	0.9	(e)	0.9	(f)

1. For sections classified as transition, it shall be permitted to use φ corresponding to compression-controlled sections. 2. ε t * is the greater of net tensile strain calculated for P n = 0.1A g f ′ c and 0.005. 3. For sections with factored axial compression force P u ≥ 0.1A g f ′ c , φ shall be calculated using equation (c) or (d) for sections classified as transition, as applicable.

1905A.1.14 ACI 318, Section 24.2.1. Add Section 24.2.1.1 to ACI 318 as follows:

24.2.1.1 – Span to depth ratio. Prestressed beam and slab span to depth ratios for continuous prestressed concrete members shall not exceed the following, except when calculations of deflections and vibration effects prove that greater values may be used without adverse effects:

Beams ......................................30

One-way slabs .........................40

Two-way floor slabs ................40

Two-way roof slabs .................44

These ratios should be decreased for special condi- tions such as heavy loads and simple spans.

Maximum deflection criteria shall be in accordance with ACI 318 Section 24.2.2.

1905A.1.15 ACI 318, Section 26.12.2.1(a). Replace ACI 318 Section 26.12.2.1(a) by the following:

26.12.2.1(a) Samples for strength tests of each class of concrete placed each day shall be taken not less than once a day, or not less than once for each 50 cubic yards (345 m ³ ) of concrete, or not less than once for each 2,000 square feet (186 m ² ) of surface area for slabs or walls. Additional samples for 7-day compres- sive strength tests shall be taken for each class of con- crete at the beginning of the concrete work or whenever the mix or aggregate is changed.

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CONCRETE

using the delivery equipment selected and shall result in finished in-place hardened shotcrete meeting the strength requirements of this code.

1908 A .3 Aggregate. Coarse aggregate, if used, shall not exceed ³ /4 inch (19.1 mm). For structural walls, when total rebar in any direction is more than 0.31 in ² /ft. or rebar size is larger than No. 5, shotcrete shall conform to course aggre- gate grading No. 2 in accordance with Table 1.1.1 of ACI 506R.

1908 A .4 Reinforcement. Reinforcement used in shotcrete construction shall comply with the provisions of Sections 1908 A .4.1 through 1908 A .4.4.

1908 A .4.1 Size. The maximum size of reinforcement shall be No. 5 bars unless it is demonstrated by preconstruction tests that adequate encasement of larger bars will be achieved.

1908 A .4.2 Clearance. Where No. 5 or smaller bars are used, there shall be a minimum clearance between parallel reinforcement bars of 2 ¹ /2 inches (64 mm). When bars larger than No. 5 are permitted, there shall be a minimum clearance between parallel bars equal to six diameters of the bars used. Where two curtains of steel are provided, the curtain nearer the nozzle shall have a minimum spacing equal to 12 bar diameters and the remaining curtain shall have a minimum spacing of six bar diameters.

Exception: Subject to the approval of the building official, required clearances shall be reduced where it is demonstrated by preconstruction tests that adequate encasement of the bars used in the design will be achieved.

1908 A .4.3 Splices. Lap splices of reinforcing bars shall utilize the noncontact lap splice method with a minimum clearance of 2 inches (51 mm) between bars. The use of contact lap splices necessary for support of the reinforcing is permitted where approved by the building official, based on satisfactory preconstruction tests that show that adequate encasement of the bars will be achieved, and provided that the splice is oriented so that a plane through the center of the spliced bars is perpendicular to the surface of the shotcrete.

1908 A .4.4 Spirally tied columns. Shotcrete shall not be applied to spirally tied columns.

1908 A .5 Preconstruction tests. A test panel shall be shot, cured, cored or sawn, examined and tested prior to commencement of the project. The sample panel shall be representative of the project and simulate job conditions as closely as possible. The panel thickness and reinforcing shall reproduce the thickest and most congested area specified in the structural design. It shall be shot at the same angle, using the same nozzleman and with the same concrete mix design that will be used on the project. The equipment used in preconstruction testing shall be the same equipment used in the work requiring such testing, unless substitute equipment is approved by the building official. Reports of preconstruction tests shall be submitted to the building official as specified in Section 1704 A .5.

1908 A .6 Rebound. Any rebound or accumulated loose aggregate shall be removed from the surfaces to be covered prior to placing the initial or any succeeding layers of shotcrete. Rebound shall not be used as aggregate.

1908 A .7 Joints. Except where permitted herein, unfinished work shall not be allowed to stand for more than 30 minutes unless edges are sloped to a thin edge. For structural elements that will be under compression and for construction joints shown on the approved construction documents, square joints are permitted. Before placing additional material adjacent to previously applied work, sloping and square edges shall be cleaned and wetted.

rein, unfinished work shall not be allowed to stand for more than 30 minutes unless edges are sloped to a thin edge. For structural elements that will be under compression and for construction joints shown on the approved construction documents, square joints are permitted. Before placing additional material adjacent to previously applied work, sloping and square edges shall be cleaned and wetted.

The film of laitance which forms on the surface of the shot- crete shall be removed within approximately two hours after application by brushing with a stiff broom. If this film is not removed within two hours, it shall be removed by thorough wire brushing or sand blasting. Construction joints over eight hours old shall be thoroughly cleaned with air and water prior to receiving shotcrete.

1908 A .8 Damage. In-place shotcrete that exhibits sags, sloughs, segregation, honeycombing, sand pockets or other obvious defects shall be removed and replaced. Shotcrete above sags and sloughs shall be removed and replaced while still plastic.

1908 A .9 Curing. During the curing periods specified herein, shotcrete shall be maintained above 50°F (10°C) and in moist condition.

1908 A .9.1 Initial curing. Shotcrete shall be kept continuously moist for 24 hours after shotcreting is complete or shall be sealed with an approved curing compound.

1908 A .9.2 Final curing. Final curing shall continue for seven days after shotcreting, or for three days if highearly-strength cement is used, or until the specified strength is obtained. Final curing shall consist of the initial curing process or the shotcrete shall be covered with an approved moisture-retaining cover.

1908 A .9.3 Natural curing. Natural curing shall not be used in lieu of that specified in this section unless the relative humidity remains at or above 85 percent, and is authorized by the registered design professional and approved by the building official.

1908 A .10 Strength tests. Strength tests for shotcrete shall be made in accordance with ASTM C1604 by an approved agency on specimens that are representative of the work and that have been water soaked for not fewer than 24 hours prior to testing. Where the maximum-size aggregate is larger than 3/8 inch (9.5 mm), specimens shall consist of not less than three 3-inch-diameter (76 mm) cores or 3-inch (76 mm) cubes. Where the maximum-size aggregate is ³ /8 inch (9.5 mm) or smaller, specimens shall consist of not less than 2inch-diameter (51 mm) cores or 2-inch (51 mm) cubes.

1908 A .10.1 Sampling. Specimens shall be taken from the in-place work or from test panels, and shall be taken not less than once each shift, but not less than one for each 50 cubic yards (38.2 m ³ ) of shotcrete.

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1908 A .10.2 Panel criteria. Where the maximum-size aggregate is larger than ³ /8 inch (9.5 mm), the test panels shall have minimum dimensions of 18 inches by 18 inches (457 mm by 457 mm). Where the maximum-size aggregate is ³ /8 inch (9.5 mm) or smaller, the test panels shall have minimum dimensions of 12 inches by 12 inches (305 mm by 305 mm). Panels shall be shot in the same position as the work, during the course of the work and by the nozzlemen doing the work. The conditions under which the panels are cured shall be the same as the work. Approval from the enforcement agency shall be obtained prior to performing the test panel method.

1908 A .10.3 Acceptance criteria. The average compressive strength of three cores from the in-place work or a single test panel shall equal or exceed 0.85 f ′ c with no single core less than 0.75 f ′ c . The average compressive strength of three cubes taken from the in-place work or a single test panel shall equal or exceed f ′ c with no individual cube less than 0.88 f ′ c . To check accuracy, locations represented by erratic core or cube strengths shall be retested.

1908A.11 Forms and ground wires for shotcrete.¶

Forms for shotcrete shall be substantial and rigid. Forms shall be built and placed so as to permit the escape of air and rebound.

Adequate ground wires, which are to be used as screeds, shall be placed to establish the thickness, surface planes and form of the shotcrete work. All surfaces shall be rodded to these wires.

1908A.12 Placing.¶

Shotcrete shall be placed in accordance with ACI 506R.

[DSA-SS] Exception: The reference to ACI 506R shall be to ACI 506.2 and ACI 506R.