Case Study: PV Plant Concrete Cabins Presented by: Justin Kretzmar Rocla (ISG)

ISG – Infrastructure Specialist Group

Started at Rocla in 2010 New product development, marketing and sales Started at Rocla in 2012 Research, development and implementation of SCC at Rocla Jason Roberts BTech (Civil) Justin Kretzmar BSc Eng (Civil)

What is SCC? SCC refers to a Self-compacting concrete, that: fill air voids, without segregation and excessive bleeding, * without vibration. Self-compacting Concrete (SCC)

Goals recognised for moving towards SCC Time and Cost Savings Zero Vibration (Energy Saving) Less-Engineered Moulds More Complex Product Designs Improved Safety and Work Environment Labour Efficiencies * Improved Concrete Quality Self-compacting Concrete (SCC)

Alfabloc Portable Security and retaining wall blocks SCC Required for New Products REBLOC New road barrier system licensed from Austria Wingwalls Improves Inlet and outlet hydraulics to a pipeline Mini Alfabloc 2.1m in Height 584 liters of Concrete Required Cast Time: 132 seconds

Initial Challenges Recognised Old traditional pan mixers installed SCC traditionally sensitive and repeatability is difficult Ideal SCC is designed around a holistic approach Assisted by CCE lab using M&R ARC technology Transport complications * Discharge complications Initial Challenges and Problems

Initial Problems Encountered Insufficient Mixing Energy Poor Repeatability with various Chemical Suppliers Average Quality and Strengths Initial Challenges and Problems Where to from here?

Roodepoort Preliminary Successes

Virginia Preliminary Successes

Reasons for Success Understanding how SCC works Trying different mould release oils Minimising vibration during transport Maintaining a constant cast rate Ensuring that the moulds were properly clean * Educating the labour about this new concept Preliminary Successes

Polokwane Repeatability was an issue Old pan mixers have a tendency to leak, causing paste loss Aggregates not ideal for SCC Method of transportation * Method of discharge Initial Failures

Concrete Cabins Solar Project 128 MW (130,000 houses) 128 Cabins in Total Cabins on Site

Concrete Cabins Solar Project Inverters Transformer Switchgear

Concrete Cabins Solar Project Cabin Size 8.7m x 2.6m x 3.1m Volume and Mass (individual) Shell: 18 Tons Volume and Mass (complete) Complete Cabin: 28 Tons Mass Delivered Electronics included: 38 Tons Concrete Cabins

Concrete Requirements Strength Requirements 40MPa at 7days Minimum of 18MPa at 16 hours Quality Requirements Provide concrete testing certification Architectural finish Production Schedule Requirements One complete cabin per day Challenges Highly reinforced thin walled sections Wall thickness ranged from 40 – 100mm

Pumped SCC High early strengths at 18MPa for stripping Entirely eliminate honeycombing and requirement for patching/painting Glass-like finish Updated SCC Requirements

Problems Encountered Pump blockages Pinholes and Blowholes Pullouts Bleeding and Segregation Low Early Strengths First Cabin Cast

Design a more robust SCC Changed the aggregate proportions Increased the cementitious content Reduced the additive content Manage the pumping rate to avoid segregation of the mix Reduce stripping time Overall quality improvements were required Back to the Drawing Board

Minor pump blockages Pipeline maintenance and layout is critical Still low early strengths Pinholes and Blowholes Pullouts The Outcome

Introduced a hardening accelerator from Mapei at 1.5% of the cementitious content The Outcome Consistency of the SCC seemed to have changed Stripping strengths at 16hours were achieved Product quality reduced Pinholes and Blowholes still visible Pullouts still occurred Mix Design III

Reduced the accelerator to 1% in hope to improve product quality The Outcome The workability seemed to have improved Stripping strengths reduced, causing delays Pinholes and Blowholes still visible Pullouts still occurred Introduced steam curing Mix Design IV

Called in CCE Laboratory to analyse the SCC design and to comment on site procedures The Outcome Increased the filler sand and reduced the stone Cast from two positions only Near perfect product achieved Pullouts still occurred Areas of minor honeycombing occurred Mix Design V

Experimented with 4 different mould oils and 3 methods of application Mould modifications and maintenance to reduce pullouts Adjusted spacers and placement to eliminate honeycoming More stringent moisture checks with mixer operator Final Changes Introduced

The Outcome