For decks and slabs, the concrete surfaces shall be protected immediately after screeding and finishing operations are progressively completed in order to minimise evaporative moisture losses, until curing by one or a combination of the methods specified in Clause610.23 is implemented. compressive stress limit for concrete at release for post-tensioned WebThe causes of time dependent/long-term loss include creep and shrinkage in concrete, and tendon relaxation. Further information is contained in Reference 4. investigate concrete deck slabs for fatigue. Restraint to this contraction can lead to cracking in the surface layers. The test certificates of compliance shall relate only to the formulation on which the tests were made and shall be valid for not more than three years from the date of issue. X". compressive stress in the node regions should be verified for HSC. Bridges and multi-storey car parks have been particularly exposed to de-icing salts. 610.17 TEMPERATURE, EVAPORATION LIMITS AND CONCRETING OPERATIONS (a) General All freshly finished concrete surfaces shall be protected where required from the sun, wind or rain, until curing is implemented. Ductile failure modes are much safer as they give greater deflections and thus more warning before failure. cracking moment may be very close to or even higher than the For lightweight concrete, loss of prestress shall be based on the representative properties of the concrete to be used. [Equation 68], (5.8.3.3-2) or by reinforcing bars where all steel in contact with concrete is Cores shall not be cut from prestressed concrete after the prestressing force has been applied or transferred to the concrete, unless the proposed coring is certified by the proof engineer. The core holes shall be cleaned and repaired with a shrinkage compensating polymer modified cementitious repair material in accordance with the requirements of Section689. Risk Diagnostics and Benchmarking Why do it? stress at ultimate as a function of c. This requires 4.8.2 Forces on connections. The Contractor shall maintain records of dimensional measurements to demonstrate that all completed concrete members comply with the allowable dimensional tolerances as stated in this clause. Application of the evaporative retarding compound shall be implemented in accordance with the manufacturer's instructions. HP Concrete shall not be placed until: (i) the Contractors WMS, ITPs and quality control checklist(s) have been reviewed by the Superintendent (ii) the evidence that the forms, reinforcement, any stressing materials and embedments conforming to the requirements of this specification and the drawings, has been reviewed by the Superintendent (iii) all foreign material has been completely removed from the forms (iv) the Contractor submits documented evidence of conducting tool box meetings of all concrete construction personnel on all aspects of the WMS, the ITPs, quality control checklist(s) and all specification requirements (v) the Contractor submits a site sampling and testing procedure in accordance with the minimum frequency of testing requirements of this section for assurance of concrete quality, and as stated in Clause610.16(b), Clause610.16(c) and Clause610.16(n), including superplasticised concrete and SCC. Cylinders shall be transported to the testing laboratory in moisture proof containers. No nasties. It is primarily caused by the rate of water evaporation exceeding the rate of bleeding. Continuous bar chairs shall provide a minimum gap between the formwork and the underside of the bar chair voids of 1.5times the maximum nominal size aggregate in the concrete mix. Where a hydration control admixture is added to the concrete mix to delay hydration the stated extended discharge time shall not be exceeded. Concrete shall not be mixed when the air temperature is lower than 5C or greater than35C. The end result of the project is stated under the This information shall be used in conjunction with Figure610.171 to determine the rate of evaporation of water from the freshly placed and unprotected surface of the concrete. to the equation for the modulus of rupture and/or the 1.2 factor shall be taken as: The coefficient of 0.85 needs to be verified for HSC. concrete. Non-destructive tests may be used to determine the insitu strength of suspect concrete subject to approval by the Superintendent. The Contractors construction quality procedure and inspection and test plan(s) shall address as a minimum the distance from the source of vibration, the intensity and duration of vibration, and the nature of the medium or underlying soil type through which the vibration is travelling. proposed. Cementitious mortars and grouts shall have a minimum 28 day compressive strength of not less than 40MPa. In prestressed concrete structures, the initial tension is reduced due to the effect of the creep and shrinkage of concrete, so the reduced relaxation should be used in consideration of the reduced tension. Water/Cementitious Material (W/C) Ratio: The ratio of the amount of water to the total amount of cementitious materials by mass in a freshly mixed cubic metre of concrete. Vibration shall be applied to the full depth of each layer and extended into the top 100mm of the underlying layer. (f) Rejection of Surfaces Finishes Any concrete surface that does not comply with the requirements of this specification shall be subject to the following alternatives: (i) rejection of the concrete, in which case the concrete shall be demolished and replaced (ii) acceptance of the defective concrete surface will be withheld subject to remedial measures being carried out in accordance with Clause610.32. WebAnchorage A device or provision enabling the prestressing tendon to impart and maintain the prestress in the concrete. WebACI 318 -05 is the American Concrete Institute code, is outdated, there are new updated versions. The reaction product is a gel which swells as it takes in pore water. The size of ducts shall not exceed 0.4 times the least gross Both the visual inspection and slump estimate shall be carried out prior to the addition of any water which may be added on site and prior to any addition of a superplasticiser. Table 5.9.4.2.2-1. Upper surfaces of concrete bearing pedestals shall have a Class2 surface finish. The repair of concrete cracks shall be in accordance with Section687. (5.4.2.1). lost may not be appropriate for HSC. fpu, the average stress in prestressing steel, fps, may be taken as: The equations in this article are based on the assumption of a (ii) Specific Requirements Curing compounds shall not be used on concrete decks or slabs, unless an aliphatic-alcohol based evaporative retarding compound is also applied after initial screeding in accordance with Clause610.17(f). Considering these topographical conditions, a method designed so that the difference in slope deflection is less than that of a partially articulated bridge is when an independent Gerber is hung in the middle of a span. known to have proportionately higher tensile strength than Placing of concrete in bored piles, underwater or in a dry bore shall be carried out in one continuous operation by tremie methods in accordance with Section606. Fig. Strength in excess of 3.50 ksi at the time of prestress. Impact of deterioration on the safety of concrete structures what can designers do to minimise risk? shrinkage of HPC with its different constituent materials. used to determine if a given source of aggregate can be safely used The accuracy of all weighing and metering equipment shall comply with the requirements of Section3 of AS1379. This affects column behavior. of an uncracked section at a stress of 0.5 f. For components with bonded prestressing tendons or In the event that the above requirements are not satisfied, application of prestress shall be deferred until such time as the compressive strength of an additional cylinder per sample achieves the specified compressive strength for pretensioned concrete or the cylinders tested at 28days satisfy the requirements of Clause610.16(g) for posttensioned concrete. Box girders or voided slabs shall be cast in longitudinal segments with a maximum segment length of 25metres. The Contractor shall not proceed with the placement of concrete until the hot or cold weather concreting procedure has been reviewed and approved by the Superintendent. use with HSC. be taken as 0.85 for concrete strengths not exceeding 4.0ksi. Eventually these particles are loosened to the extent that they fall out. For concrete structures located in marine and other saline environments or which are subject to sulphate and chemical attack at least two cylinders per sample shall be tested for VPV at 28days as detailed in Clause610.16(b) and Table610.161. If cracking does occur, it will be aligned at right angles to the restraint. axis where the approximate stress distribution specified in Article Torn or punctured sheeting shall not be used. Specifications deals with concrete structures. ASCE (American Society Civil Engineering) - SEI (Structural Engineer Institution) Standard 7 - 10 is an outdated prescribed code for Minimum Design Loads for Buildings and Other Structures, is a very good reference for work. The contract documents shall prohibit the use of aggregates from HSC is Loss of bond between steel and concrete is a result of cracking along the line and a reinforcing bar. Flexural stresses result from the bending of a member. reinforcement that are subjected to severe corrosion Bonded reinforcement sufficient to carry the calculated Should the strength of any one sample representing the concrete fall short of the specified minimum 28day compressive strength as shown in Table610.051, the concrete represented by that sample may be rejected or the Contractor may elect to test concrete cores subject to approval by the Superintendent. The results are coating, shall be 1.0 inch. Thus, the equation for appropriate coefficient for use with HSC needs to be determined. In Post-tensioning, the steel tendons are tensioned after the concrete has been cast and hardened.. Post-tensioning is performed by two main operations: tensioning the steel wires or strands by hydraulic jacks that stretch the strands while bearing against the ends of the member and then replacing the jacks by permanent Due to its thickness (90% of the secondary cell wall) and low value of microfibril angle, the S2 layer is responsible for the high tensile strength and stiffness and low shrinkage of wood in the longitudinal direction. For HPC, testing should be conducted or field experience should be The basic tension development length, ldb, in inches, shall be taken as: This article contains provisions for the development length of Furthermore, statically indeterminate forces due to longitudinal temperature changes, creep, and drying shrinkage do not occur. 5.10.2.1 shall not be less than: Basic development length, lhb, for a hooked bar with is reported by ACI Committee 363 and should be The cement paste is gradually scaled away by this freezing and thawing action. Table 610.051Concrete GradeMinimum Compressive Strength (MPa)3 days7 days28 daysVR330/32142032VR400/40172640VR450/50233550VR470/55254055 For concrete grades with minimum 28 day compressive strength in the range of 60MPa to 100MPa the minimum 3day and 7day compressive strength shall be 45% and 75% respectively of the minimum 28day compressive strength. representative properties of the concrete to be used. A proportion of any reduction in load-carrying capacity can be offset against the chemical prestress developed as a result of restraint to expansion. be taken as specified in Article 5.10.11.4.1e. The rate of evaporation shall be monitored by the Contractor until such time as curing commences. The design of the formwork shall be such as to give a deflection under the loads imposed on it of not more than the following: (i) 1.5mm between adjacent framing members (ii) 3mm over the vertical face for the full depth of a panel, or height of a lift, whichever is the lesser (iii) 3mm over a 3m length horizontally. The maximum amount of prestressed and nonprestressed reinforcement (c) Extended Protection of Concrete During the Curing Period Formwork shall be kept in place for the minimum period in accordance with the requirements of Clause610.25 prior to removal. 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