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Readymix Awards Celebrate Concrete Excellence - 2016

Monday, 16 January 2017  
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The 2016 NZRMCA Awards were presented recently at the New Zealand Concrete Industry Conference held at the Ellerslie Events Centre in Auckland. As with previous years the entries were outstanding and the winners exceptional.

Technical Excellence Award Winner 
Firth Industries for the University of Canterbury Structural Engineering Laboratory Project

Challenging construction projects, coupled with a consultative construction methodology provide a real opportunity for a concrete supplier to develop innovative technical solutions. The University of Canterbury Structural Engineering Laboratory strong floor/wall is an example of such an opportunity.

The challenges for Dominion Constructers were considerable. Extremely congested reinforcement, high strengths, tight tolerances (+/-2mm),significant depth (2m) and large pours were just a few of the obstacles that required innovative concrete solutions in order to be overcome. 

A series of three concrete mixes were formulated and trialled which were designed to be supplied in one continuous operation of 970m3. The lowest layer being a self-consolidating concrete designed to cover the first 300mm of the pour, in a zone of considerable congestion where traditional vibration was impractical. In addition to the rheological properties, the mix needed to be able to be delivered in short cycles, in large volumes and remain open for layer 2.

Layer 2, the bulk of the 2m pour, needed to minimise heat of hydration, achieve compressive strength of 40MPa, be workable and pumpable, and allow placing teams to work quickly. It also had to remain open for layer 3.

Layer 3, the upper 300mm, had to achieve high strength (65MPa), be compatible with the previous concretes, be pumpable in great volumes (a challenge for high strength mixes), and have sufficient bleed to accommodate the challenging placing conditions of Christchurch in spring.

Technical innovation was also required in providing advice on the construction methodology. Models were developed to predict the likely temperature rise in the three layered system, what type of curing would be best, whether insulation was required, and when insulation could be removed.

A critical success measure was that the crushing strength of the concrete around the numerous inserts had to be greater than the shear capacity of the bolt inserts. The contractor developed a solution to maximise the sleeve diameter, however finite element modelling (verified through full scale test blocks) still demonstrated that 65MPa concrete was required. It was imperative that the shear tests were conducted at a time when the concrete had reached the desired strength. This involved monitoring of the temperature of the concrete, using temperature matched curing for test cylinders, and developing a maturity model to predict when would be the most appropriate time to test the concrete cylinders.

Further technical excellence was offered by the construction of the walls. The reinforcement was very congested, and high strength concrete was needed around the inserts. However, the option did not exist for the three layer solution. The challenge for Firth was to develop a concrete mix which would keep temperatures below a maximum, but achieve the greatest possible strength. Heat of hydration models were developed, calibrated against the floor, modified to accommodate different boundary conditions, and then a suite of concrete solutions modelled. The chosen solution was trialled to confirm the thermal performance and the desired hierarchy of bolt failure.

2016 NZRMCA Technical Excellence Award winners Nan Jiang, Dene Cook and Dominic Sutton of Firth Industries, flanked by Grant Thomas and Daniel Douglas of Dominion Constructors Ltd

Extra Distance Award
Allied Concrete for Curvey Basin Chairlift & Remarkables Ski Field Base Building

Over two years in the off season, Allied Concrete supplied over 2,900m3 of concrete for the new Curvey Basin Chairlift and Remarkables Ski Field Base Building.

The majority of the concrete supplied was a 30MPa 6% air entrained mix to deal with the freeze thaw conditions, and with an hour travel time was retarded.

It was a 50 kilometre round trip, with the last 13 kilometres a steep climb on an unsealed road to the existing Base Building. Access up the mountain was up an even steeper 1.6 kilometre climb on a ‘Cat Track’.

Stage 1 involved supplying concrete for 12 tower bases and two return stations on the new chair lift. Both return stations required around 75m3 of concrete in one pour. With the top station over 1,900m above sea level it could only be supplied in 3.5m3 loads due to the steep gradient of the access road. 6m3 loads were taken as far as the Base Building where they were then transferred into smaller trucks to access the top of the mountain. All the towers were accessed by truck on the mountain taking up to 20m3 per tower again in maximum 3.5m3 loads.

Stage 2 involved supplying 2,400m3 concrete for a new Base Building (1,600m3 above sea level) at the Remarkables Ski Field over a 6 month period. The biggest pours where around 100m3, but the main hurdle faced on Stage 2 of this project was the weather.

Once the Remarkables Ski Field had closed at the end of the 2014 season and excavations had begun for the new Base Building the mountain was hit by frequent weather systems that included numerous snow days. During the last month of the project winds regularly reached up to 150kph. In total, 42 days were lost to inclement weather
on the project.

There were at least four occasions when trucks were lowered off the mountain tethered to a 17 tonne loader equipped with a full set of ice breaker chains.

During the last month of the project Allied Concrete Queenstown was required to work 21 days straight to complete this project as there was a real danger that the Base Building would not be finished for the new season, meaning the ski field would have remained closed for the 2015 season.

This required careful management of staffing levels to not only supply the project but also maintain supply to other customers over a very busy period. Compliance with all heavy license restrictions, driver hours and days off were also non-negotiable.

Another issue that caused problems over both stages of the project was the deterioration of the ski field access road. High volumes of heavy vehicles throughout the build caused massive corrugations in the road which on the return trip with an empty truck led to a number of issues with the fleet.

John Benn and James Mackechnie of Allied Concrete 

NZRMCA Plant Audit Scheme Supreme Award
Atlas Concrete - Takapuna Plant

Quality assurance was the primary reason for the establishment of the NZRMCA and the development of the Plant Audit Scheme many decades ago.

NZRMCA Honorary Life Member Maurie Hooper presents Sabina Sekerovic of Atlas Concrete with the 2016 Plant Audit Scheme Supreme Plant Award

The independent Scheme remains the cornerstone of the Association. The judging criteria for this Award acknowledge consistently high performance over an extended period of time.

In producing large quantities of concrete to a reliably high quality across a number of years Atlas Concrete’s Takapuna plant has demonstrated continuing excellence in performing to NZS 3104 Specification for Concrete Production.

The judges highlighted the fact that this plant had received Excellence Awards in each of the last 5 years, which is indicative of the attention to detail shown by the concrete production management team.

The plant is an example to all other ready mixed concrete producers across New Zealand.