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Concrete In Australia : June 2014
Concrete in Australia Vol 40 No 1 7 The two beams tested with a/d ratios of 2.0 had concrete strengths of 26.8 MPa and 24.8 MPa and once again the beam with the lower concrete strength had the larger bearing length (152 mm) and displayed the higher shear capacity (22% higher in this case). 3. We agree with Mr McBride that an engineer designing a new beam with shear reinforcement would ensure that minimum shear reinforcement be provided. However, if the engineer is evaluating the shear capacity of an existing beam the option of choosing the shear reinforcement is not available. As requirements for minimum amounts of shear reinforcement were only introduced in the 1970s, many older reinforced concrete structures contain amounts of shear reinforcement which do not satisfy current minimum requirements. 4. Yes, the terms in the bracket just above Equation 1 should have read (fc =0.65, f s = 0.85). 5. Because the beneficial effects of minimum shear reinforcement increase substantially with increase in member thickness, the authors recommend that at least a minimum quantity of shear reinforcement be provided in the flexural regions of slabs and beams with an overall thickness greater than 750 mm. If such reinforcement had been provided in the Concorde Overpass the catastrophic shear failure discussed would not have occurred. Geopolymers The March 2014 edition of Concrete in Australia featured three technical papers on geoploymers. Clearly, the introduction of geopolymers is being heralded as a fantastically innovative solution to help address the perceived sustainability liabilities of Ordinary Portland Cement (OPC). But before we get too carried away with specifying its use in more widespread applications, at least some consideration should be given to constructability aspects. Of particular interest to practitioners in the field are the setting and workability characteristics, and vitally, the ramifications on formwork designs pertaining to concrete using geoploymers. Much published research has understandably focused on determining structural equivalence of the emerging technology with OPC concretes. For instance, 28 day strength comparisons. However, there remains a pragmatic imperative to ascertain how geopolymers will affect the work of contractors using it in situ. Granted, at p42 the authors state that “geopolymer concrete could be handled and finished similarly to normal concrete”. This is construed predominantly in a precast (ie controlled) scenario, and for what I can see, applying to relatively flat elements. From our perspective, answers to other genuine constructability concerns are required: How applicable is AS3610? What concrete pressure assumptions should engineers in our industry be making? Do we know how workability and setting characteristics of geopolymers will affect the constructability of these concretes? Will the expectations of architects and consultants be satiated by the realities of what is actually constructible? Sustainability of concrete as a construction material necessitates a more holistic approach than merely securing a substitute for Portland cements. It is safe to assume that concrete constructors look forward to future geopolymer developments with more than a little trepidation. Carlo Garofali BE(Civil), DipLaw(LPAB), MIEAust, CPEng Engineering Manager, PERI Australia The Concrete Institute’s educational programs aim to increase knowledge through the dissemination of fundamental and applied information for the benefit of the concrete and construction industry in general. Keeping abreast of the latest issues and developments within the dynamic fields of engineering and concrete technology is crucial, and this is why professional bodies mandate Continuing Professional Development (CPD). The Concrete Institute conducts regular seminars, technical evenings and site visits around Australia – most of which count fully toward relevant CPD requirements. Visit the Institute’s web-site to browse for educational programs in your State, or for news on National programs that are of interest to you. Save while you accumulate CPD Hours Concrete Institute Members benefit from significant discounts on registration fees for the Institute’s Educational Programs. Membership is generally tax-deductible, so join today and start solving the CPD puzzle. www.concreteinstitute.com.au SOLVE THE CPD PUZZLE 06-07 - Letters.indd 7 06-07 - Letters.indd 7 22/05/14 11:42 AM 22/05/14 11:42 AM