Concrete Offers Myriad Advantages

Concrete Offers Myriad Advantages

Due to its durability, versatility, aesthetic appeal, cost-effectiveness and availability, concrete is changing the face of South Africa’s landscape with cutting-edge architects and engineers increasingly making concrete their material of choice.

Concrete is the most economical choice for engineered structures, says TCI MD Bryan Perrie

Here, Bryan Perrie, MD of The Concrete Institute, (TCI) deals with the benefits of the world’s oldest and most popular building material:

Economic benefits:

Due to its longevity and ease of construction, concrete is often the most economical choice for engineered structures. Load-bearing concrete exterior precast or tilt-up walls serve not only to enclose the buildings, but to carry roof and wind loads – eliminating the need to erect separate cladding and structural systems.

Lower energy costs:

The energy efficiency of a structure is a major consideration in the life cycle cost analysis. Concrete construction can minimise the overall building height to shorten vertical runs of mechanical and electrical systems and reduce the exterior surface area to be enclosed and insulated.

Insulated concrete buildings with a medium to high level of thermal mass are characterised by their inherent ability to store thermal energy, and then release it several hours later when needed.

Faster turnaround:

Once the design has been selected, there is generally pressure to get a project started. More and more organisations are making speed a priority, particularly high technology companies and rapidly growing firms. When such businesses decide to construct a new facility, they are often overburdened and already behind schedule. With concrete designs, there is no delay in getting started as concrete is readily available from many locations across South Africa. A concrete structure can be well underway using in-situ concrete before final plans are complete. Precast/prestressed concrete can also help reduce construction time and on-site labour costs by taking advantage of pre-fabrication of standard and custom structure segments.

From multi-billion rand massive dams to simple low-cost housing schemes, concrete is the logical choice

Advanced construction techniques such as ‘flying formwork systems’, increase the speed of floor construction. As a concrete frame progresses upward, workers on the completed floors below can proceed with interior partitions, exterior finishing, electrical, mechanical and plumbing systems.

Generating revenue faster:

Faster construction means reduced carrying costs and faster revenue generation. This facilitates more timely pay back of financing charges and faster revenue generation for the developer/owner.

Versatility:

The design flexibility of concrete allows the contractor to accommodate design changes after the process has begun.

Design and colours:

Limited only by a designer’s imagination, the breadth of designs, colours and textured finishes available in concrete today is unrivalled. Mixing and matching colours and textures provides a spectrum of design possibilities.

Textures:

Concrete textures can resemble smooth, high-polished granite or gutsy, exposed aggregates with a rugged feel. Other possibilities include tumbled cobblestone, brick, cultured limestone, slate, flagstone or river rock.

Stamping and scoring:

As natural stone becomes inaccessible or the costs rise prohibitively, concrete is a natural alternative for recreating traditional finishes in a cost-effective way. Besides being widely available and less expensive than quarried stone, cement-based cultured stone is easier to match and install. This makes it popular even in places where quantities of quarried stone are available.

Reduced sound transmission:

Containing sound within the walls of a structure is critical in today’s highly competitive environment. Should the tenant requirements include sound transmission control, the natural mass of concrete floor and wall systems provides both acoustical resistance and vibration control.

Creative wiring options:

Thin concrete floor structures facilitate the use of raised floor systems used where the wiring is run in the space below.

More floors per structure:

Shallower floor systems are an important structural advantage of concrete. On average, the construction of concrete buildings will allow one additional floor to be created for each 10 storeys of traditional building height, resulting in more rentable space for buildings of similar size. When faced with height restrictions, concrete construction is a key consideration and could represent initial construction cost savings and additional income generation. Longer spans:

Post-tensioning reinforced concrete beams and slabs allow for longer floor spans with fewer columns to plan around. This offers flexibility in architectural layout and even more usable space. Increasingly, concrete is setting the standard for space planning and utility infrastructure.

Fire resistance:

The range of designs, colours and textured finishes available in concrete is limited only by a designer’s imagination

Concrete is often left exposed on interior walls due to its aesthetic appeal, durability and inherent fire-resistance.

Ideal for strict specifications:

A major advantage of concrete construction for engineered structures is the material’s properties of density and mass. Lateral stiffness, or resistance to horizontal movement, make concrete the product of choice when constructing tall buildings where high winds or seismic conditions are considerations. This lateral stiffness also means that occupants of concrete towers are less able to perceive building motion.

Energy efficiency:

Most concrete is produced locally, minimising fuel requirements for handling and transportation. Once in place, concrete offers significant energy savings over the lifetime of the structure. The mass of a concrete structure makes it a significant thermal reservoir with the ability to store large amounts of energy. In hot months, concrete walls and floors absorb the interior heat during the day, then radiate warmth back into the space at night. The same principle holds true for cooling. This thermal inertia allows concrete to help maintain a relatively steady interior temperature.

Recycling:

Concrete is an inert material that is easily recyclable. Old concrete that has reached the end of its service life can be reused as aggregate for new concrete mixtures. The addition of industrial by-products such as fly ash, silica fume and blast furnace slag make concrete less permeable while incorporating materials that would otherwise be deposited in landfill sites.

AST Sand Mines announces a “maiden” quartzite resource to supply roadstone and silica sand to the infrastructure and construction sectors in East Pretoria and the Moloto corridor

AST Sand Mines announces a “maiden” quartzite resource, strategically located to supply roadstone and silica sand to the infrastructure and construction sectors in East Pretoria and the Moloto corridor in KwaMhlanga

Van Dykspruit quarry, owned by AST and located on the Gauteng and Mpumelanga provincial border, declared its maiden quartzite-roadstone resource recently as management initiated their inaugural blast to access the underlying high grade quartzite rock. The quartzite will be processed to supply roadstone to the nearby Moloto corridor project in KwaMhlanga.

The quarry, which has been in operation since 2012, has to date been extracting a surface level resource of weathered sandstone which is processed with state-of-the-art wet screens that produce high grade silica which is supplied to clients such as Petra’s Cullinan diamond mine for use in underground structural concrete.

AST’s managing director, Ian Ross, said: “We have developed this mine over the past 7 years from a greenfield start, to become a fully operational quarry that is now positioned to become a strategic supplier of roadstone and high grade silica for the construction and infrastructure market in North and East Pretoria, and KwaMhlanga.”

Current production capacity is 30 000 tonnes per month, and the mine is delivering a 98% silica sand product, with run-of-mine passing 8mm and 13% passing 75μ. After processing, the mine’s standard grade of product is delivered at -8 mm /+75μ, carrying an average 2.5% of sub 75 μ material, which allows clients to receive a consistently graded product at volume which is suitable for making high grade structural concrete.

An extensive drilling programme and high-resolution, low-frequency Loza ground-penetrating radar survey has been completed. The resource will meet East Pretoria and KwaMhlanga’s demand for roadstone for close to a decade. Ross said: “We have been able to drill the quartzite resource with a high degree of accuracy using a new ground penetrating radar technology. This has allowed us to delineate the resource at a low cost. The recovered core has been confirmed as a high grade roadstone, and allowed us to optimise the design of the crushing circuits that will deliver the scope of material the market demands.”

DCIM/100MEDIA/DJI_0012.JPG

AST retained B&E International to conduct the inaugural drilling, and the inaugural yielded over 50 000 tons of product immediately available. Ross said, “We are now the closest operational quarry to Moloto, and we look forward to working with our clients and partners to deliver value as the Moloto development gets underway.”

 

About AST: Website: www.ast14.co.za----escape_sem_autolink_uri:6b7a36f07a51f9ea670074da1d3ea877----

AST’s Silica & Quartzite Mines
AST’s quarry mine is in production exploiting near-surface semi-consolidated sandstone lithologies. This resource sits in a small package that is a remnant of the Ecca group, consisting of sandstone, that itself overlies the Loskop formation that consists of quartzites that are a target resource for roadstone.

The silica is processed in a dry screen, and then into a wet screen. The wet screen technology, sourced from CDE in Ireland (www.cdeglobal.com) , delivers a consistent high-quality product.

The washing system produces concrete sand (coarse) and plastering sand (fine), but it can also produce a single plastering sand or concrete sand in larger quantities as required by the customer. The washed sand product is typically less than 2.6% moisture content (by weight) which ensures it is suitable for use immediately.

Environmental considerations are central to ASTs approach. The wet-screen’s waste-water treatment process reduces the volume of fresh water to feed the washing plant by over 90%. This represents a huge reduction in water usage, and the plant design is confined to a much smaller plant and mining operation “footprint” of circa 30m x 20m.

A crushing circuit will be installed and commissioned to process the quartzite at 400 tonnes per hour, with first deliveries scheduled for early Q4 2019.

Loza Radar:

(www.lozaradarafrica.co.za and http://www.worldwidegeological.com.au/index.php/loza-radar/ )

Drilling on AST’s concession has been augmented with specialist low-frequency radar surveys which show the depths of the sandstone/quartzite contact.

Loza is the world’s most powerful Ground Penetrating Radar (GPR). It delivers unrivalled high resolution imaging of the earths sub-surface to depths of over 200m. A survey using Loza radar allows for fast, accurate and non-invasive geophysical based surface exploration, and delivers instant and clear images of the subsurface.

GPR is based on “stacking” a series of ultra-wide band electromagnetic pulse emissions that are sent directly into the subsurface. The Radar captures information about the different conductive properties of the lithology directly under the device. The radar records the conductive differences, and shows – in section view – a geophysical based interpretation of different lithological interfaces, layers or objects.

The Loza radar runs over a known point of reference, in AST’s case, the drill holes, in order to calibrate the radar image. The radar can then track the sandstone and quartzite interface, allowing for a wider drill grid. This enables the client to have a wider drill grid, with calibrated Loza survey lines running across the grid.

Loza’s average daily production in non-cleared terrain is between 2.5 km and 4 km per day allowing for large survey’s to be completed in a short time frame. Importantly the acquisition of data is environmentally friendly where clearing for survey lines is not necessary.

A professional geological survey has been completed, and a Leapfrog 3D model created using drill hole and radar data.

Ideal – and essential: Introduction to Concrete

Ideal – and essential: Introduction to Concrete

The Concrete Institute’s School of Concrete Technology will this year again present a basic – but “absolutely essential” – training course in concrete technology for diverse operational levels in the construction sector.

John Roxburgh, senior lecturer at the School of Concrete Technology in Midrand, says the aptly-named two-day Introduction to Concrete course is suitable not only for emerging and new building contractors, small or medium-sized enterprises, but also for any newcomer to concrete-related work responsibilities.

John Roxburgh, senior lecturer at the School of Concrete Technology

For a start, sales and laboratory staff as well as site employees will greatly benefit from the SCT 10 Introduction to Concrete course. The training – augmented by laboratory sessions with hands-on experience – deals with essential elements of concrete operations such as getting the basics right and knowing why certain procedures and practices are required. This is essential background knowledge for anyone planning careers in concrete and concrete-related industries,” Roxburgh states. “In fact, even the most junior staff in companies in the cement and concrete sectors should be armed with the knowledge this course offers.”

He says the increasing number of emerging building contractors now entering the construction industry will also greatly benefit from the Introduction to Concrete training. “Concrete plays a major role on any construction site and needs to be placed and finished off correctly for any contract to be successful and a new company’s reputation to be established. Unfortunately, many newcomers to the construction industry tend to think that making suitable concrete is merely a matter of mixing some sand, stone and water with a bag of cement. There is far more to producing sustainable concrete than such basic knowledge.”

Roxburgh says the Introduction to Concrete course will give emerging contractors and other key players in the construction industry important information to edge out competition. “It is a course that covers all essential aspects such as the basics of materials for concrete, batching and mixing of concrete, and the necessary requirements for transporting, placing, compacting, and protecting as well as curing of concrete.”

Also included in the course are topics such as:

  • Properties of concrete;

  • Receiving and storing materials;

  • Testing of concrete;

  • Finishing and surface preparation;

  • Formwork and reinforcement;

  • Sand-cement mixes; and

  • Durability of concrete.

    The correct method of curing concrete forms part of the training in the School of Concrete Technology’s Introduction to Concrete course

For emerging contractors, an additional benefit is that one of the School of Concrete Technology’s experienced lecturers, Matthews Magwaza, can explain concrete concepts in five South African languages,” Roxburgh adds. “Our total offering for all levels of competency explains why the School has for many decades been the most respected provider of concrete technology education in South Africa.”

More details on the SCT10 course and other more advanced training from the School of Concrete Technology planned for Midrand, Cape Town and Durban this year are contained in the SCT 2019 Education Programme which can be obtained by phoning 011 315 0300 or email sct@theconcreteinstitute.org.za or visiting www.theconcreteinstitute.org.za.

AfriSam recycles concrete in its sustainability drive

AfriSam recycles concrete in its sustainability drive

Readymix concrete that is returned to the supplier for various reasons has in the past created an environmental headache, but AfriSam is now able to recycle this material for road-building purposes.

The return concrete has also been used around the readymix plant to pave large areas

While readymix suppliers must always be prepared to accommodate a certain portion of returned concrete from site when the construction schedule does not go according to plan, for instance, disposal of this material can create challenges. So, in line with its commitment to recycling in its Environmental Management Programme, AfriSam has over the years used various strategies to deal responsibly with returned concrete.

A breakthrough was made when the management team at AfriSam’s Jukskei Quarry in Midrand, Gauteng, experimented with including recycled concrete in the G5 sub-base product required for road-building. Standards permit this grade of product to comprise material from more than one source. They also require that it contain about 80% fines content which the recycled concrete was well-suited to deliver.

As a result, some 15 to 20% of the G5 product can be made up of recycled concrete, giving a good mixture of decomposed material and returned concrete. Quality remains key, and AfriSam ensures that all its products comply with the COLTO (Committee of Land Transport Officials) material grading specifications from the South African Bureau of Standards.
AfriSam’s G5 sub-base with recycled concrete was first used on the N1 highway extension work around Johannesburg – part of the Gauteng Freeway Improvement Project – and the contractor was well satisfied with it. Since then, its success has been replicated in a range of other projects.

Waste at the facility that will be recycled

The recycling process begins when the returned concrete is contained in a dedicated area of the readymix site and allowed to dry. Using a hydraulic hammer mounted on an excavator, the dry returns are broken up into chunks of 250 to 400 mm in size. After being hauled to a secondary stockpile, the material is checked and blended by plant operators before being fed into a jaw crusher.

Load-haul operators also play a role in checking that the material is within specification, and must be selective in what they bring to the stockpile to ensure blending of the appropriate quantities before crushing. Crushed material is then homogenised and stockpiled ready for use.
This innovative solution also has positive spin-offs for the readymix site itself. As there is no slush around the plant, there is less potential for contamination and a smaller carbon footprint is created. It should be remembered that no public dumping facilities would accept concrete in these quantities, making these strategic responses even more vital.

In addition to its environmental benefits, the recycling process ensures sustainability by creating a revenue stream for the recycled material; its inclusion in a saleable, quality G5 product means that it is helping offset the costs that returned concrete places on the business.

Efficient stormwater drainage solutions

Efficient stormwater drainage solutions

The Beany Block

Ineffective drainage causes a multitude of issues when areas such as roadways, parking lots, walkways and areas around buildings become swamped with large volumes of non-dispersing water. The Beany Block from Technicrete – a member of the ISG Group- is an efficient and practical solution for effective drainage due to its large flow capacity/unit weight ratio, making it a more cost-effective solution than conventional kerbing and drainage offerings.

The Beany Block system comprises a series of base blocks of standard channel section and Top Blocks of inverted channel section with an opening in one side face. When laid end to end they form a combined kerb and surface water drainage unit that is strong enough to withstand normal traffic loading.

Each standard top and base block is 500 mm in length and weighs approximately 85 kg.They have also been designed to withstand accidental 80KN axle loading. The top block oval openings provide for greater inlet capacities compared to conventional kerb inlets. Standard blocks can be used for curve radii of 30 mm or more. ‘Splay’ blocks are available to meet specific requirements with a radius of between 6 m and 30 m.

Benefits

When the Beany Block system is utilised no long drainage sections are required to be specified in contractual documents. The system can be substituted for kerbs, stormwater pipework, kerb inlets and parts of footways. Damaged services are less likely to occur when installing the Beany Block due to its simple and practical design and installation.

Some of the traditional problems experienced with conventional drainage that the Beany Block system eliminates include: insufficient fall; conflicting levels of service mains and cables; ponding adjacent to low points; traffic safety and control on existing freeways.

Additional cost savings can be achieved on projects that have wide freeways and footways; freeways that have ‘flat’ longitudinal falls; rock in sub-grade; shallow outfall and existing services or foul drainage at conflicting levels.

Applications

The Beany Block has been designed for use in conjunction with SABS Fig. 3 and Fig.4 Barrier Kerbs. The Beany produces 400 mm length of inlet opening for every 1 m of kerb. The system can be used in any application where high inlet capacity is required; wide freeways; parking areas; taxi ranks and bus depots; wash bays and vehicle service areas; median islands; industrial areas; drainage around buildings and walkways and toll plazas.

Rocla’s Stormwater pipes

Effective stormwater management can prevent pollution, flooding, erosion and damage to the environment and infrastructure. Therefore, it makes financial sense for local municipalities to invest in products and technologies to ensure that the quality of infrastructure, be it stability and sustainability of both the built and natural environments is not compromised.

Within its range of products, Rocla – also a member of the ISG Group, manufactures stormwater pipes with both interlocking and spigot and socket joints in a range of strength ratings. The spigot and socket joints utilise the rolling rubber ring principal where no installation lubricant is required. All pipes conform to the SANS 677 standard.

After consultations with Rocla’s technical team, interlocking joint pipes were selected for installation at the Great North Plaza in Limpopo, whilst the Borwa project in Westonaria selected Rocla spigot and socket joint storm water pipes. Technical support from Rocla ensures that correct product and technology is selected with consideration for the financial constraints of each project.

Technicrete is part of the IS Group of companies which includes Ocon Brick and Rocla.

A commitment cast in concrete

A commitment cast in concrete

Hannes Meyer – Cementitious Executive, AfriSam *

In April 2018, at its Peninsula Quarry operations near Cape Town, AfriSam’s top management team re-affirmed it’s long term commitment, further entrenchment and investment of assets and resources in the Western Cape.

AfriSam is renowned for its presence and dedication over decades of construction in the Western Cape, including the supply of cement, concrete and readymix for numerous iconic structures – to the benefit of the City of Cape Town, the Western Cape region and their communities as a whole.

Concrete, after water, is the most used

AfriSam plays an extensive and ongoing infrastructure development role in Cape Town and the Western Cape

product on the planet

With our considerable assets in the region, coupled with our innovative logistics operations in directing clinker from Gauteng to the Western Cape, we are able to maintain our competitive edge and deepen our commitment to Cape Town and the Western Cape,” said Hannes Meyer, AfriSam’s Cementitious Executive.

Richard Tomes, Sales and Marketing Executive for AfriSam

AfriSam’s top management team engage with the medai at the company’s Peninsula Quarry near Cape Town *

Richard Tomes, Sales and Marketing Executive for AfriSam, noted that the company is recognised as the market leader in the combined manufacture and supply of concrete materials, namely, cement, aggregates and readymix.

The AfriSam Peninsula Quarry *

We are aware of the progressive migration of people to Cape Town and the Western Cape, and note too that the turnaround of growth in construction will still take some time, however we have in place comprehensive plans for ongoing expansion in the region – to which we remain historically committed,” continued Tomes.

According to Meyer, AfriSam has in place fully approved and signed-off plans for expansion of its facilities in Saldanha Bay. This programme will build out on its existing limestone quarry in Saldanha with the addition of an EIA approved cement plant to be constructed when market conditions are favourable. “This project will enable significant expansion of all AfriSam products in the Western Cape.

Shaughn Smit, AfriSam’s National Sales Manager for Aggregates

Re-construction of the Silos is well advanced – 2016

Building on Meyer’s presentation, Shaughn Smit, AfriSam’s National Sales Manager for Aggregates, described a number of huge forthcoming developments in the Cape Town region: “AfriSam’s projected commitment programme is in direct support of the published 25 year build plan for the V&A Waterfront – where we continue to supply concrete on a daily basis; the “WES Cape” 25 year build plan (a project similar to Century City) which has already been approved by the City of Cape Town; the “Harbour Edge” development by Amdec which is in the pipeline for the Culemborg foreshore area near the Yacht Club; as well as the “joining of the bridges” which will result in another huge development below the bridges.”

De-construction and re-construction of the atrium progresses apace – 2016

Our finest example of commitment,” said Richard Tomes, “is without doubt our participation with the design of concrete for the iconic Zeitz Museum of Contemporary Art Africa (MOCAA) – the only contemporary art museum in Africa. Here AfriSam sponsored the supply of concrete at cost – and continues to play a key role as a stakeholder through active participation in educational and community programmes revolving around the museum.”

The Zeitz Museum of Contemporary Art Africa (MOCAA) and AfriSam

Project manager, Franette Ventura

A majestic work of modern engineering and concrete art

Originally completed in 1924, the 57 m high Silo dominates the Cape Town skyline.

Constructed by SA Railways and Harbours, the facility processed hundreds of thousands of tons of wheat, maize, soya and sorghum. It was sited to take advantage of its connectivity to the docks and the supporting rail infrastructure. An iconic building, it is considered an important contributor to Cape Town’s urban character.

Custom-built lifts operate inside two of the cut-away silo cylinders – servicing the six floors of art galleries above and providing visitors with a view into the atrium *

According to lead design architect, Thomas Heatherwick of the famed Heatherwick Studios in London, “We expected a rather cold surface inside the museum, but as we began to work with portions of the old concrete, we realized that it imparts a rather unique character to the building inside – a rather warm one at that.

Inside we were in danger of losing the extraordinary cellular structure, so we created a space that would help the visitor understand the building. So, you would walk in and navigate around. We took the idea of taking just one of those billions of grains of corn so that we could scale it up and use it as a model for the cutting tool to cut through.”

The cut through the concrete of the silo wall must be “like a knife through butter” – Thomas Heatherwick, architect

“like a knife through butter”

A core concept in reinforcing the strength of the remaining silo tubes so that they could be left in place and cut to the architect’s design, is the use of an inner concrete ‘jacket’. Using concrete supplied by project partner, AfriSam to engineer’s specification, the inner circumference of each silo tube was re-lined with 200 mm thick reinforced concrete to its exact cut dimension.

The top of the bins is capped with a glass roof which lets light enter the atrium from above. The bottom of the atrium is formed by graded steps that naturally contour the rounded space forming a flexible amphitheatre space that can be used for both events and displays.

In addition, a rooftop floor is dedicated to a restaurant, an education centre and a rooftop sculpture garden. It is from this level that visitors may embark on their ‘walk of faith’ across a high-performance glass floor that looks down into the atrium. Visitors arrive on this level by using one of two scenic lifts. These lifts operate inside two of the cut-away silo cylinders – with a view into the atrium. A third adjacent partly cut-away silo provides the third panoramic option – a steel spiral staircase. There are also conventional service lifts and the usual fire escape staircases, in line with standard building safety requirements.

There be Dragons in the Atrium

A spiral staircase winds up six floors to the rooftop *

This museum is a symbol and an icon of the confidence we feel about being Africans, the confidence we feel about our place in the world” said Mark Coetzee, Executive Director and Chief Curator.

 

Deep in the basement are the original silo grain release valves *

* Photos: John Thomé

Acknowledgements: Gareth Griffiths – extracts on Zeitz Museum