Developed by Intaprop and constructed by Concor, 5 Parks Boulevard is a recent addition to Oxford Parks – a vibrant mixed-use precinct being developed in Rosebank, Johannesburg. The stylish building boasts a concrete structure that was constructed at a fast track pace, in collaboration with construction materials specialist AfriSam. The Concor team accomplished a safe and on-specification result between July 2022 and Beneficial Occupation in February 2023, with the final handover in August 2023.

5 Parks Boulevard in Oxford Parks, Rosebank, is a concrete triumph of aesthetics, functionality and sustainability. The remarkable concrete picture-frame design of the building includes a striking curved slab – or ‘eyebrow’ – on two sides and over the atrium. There are also subtle but well-considered concrete edges to complement the façade on the western and north-western elevations. The building’s flush glazed and stone clad façade also contributes to its powerful visual impact.

Designed for a high (6 Star) Green Star rating from the Green Buildings Council South Africa (GBCSA), the building has a triple-volume atrium in the reception area, making the most of natural light and reducing energy consumption.

The concrete mix designs and readymix supply made an important contribution to sustainability. Mix designs reduced the project’s overall carbon footprint through the use of fly ash as a Portland cement replacement in the concrete, thereby using 30% less cement. Close collaboration between main contractor Concor and readymix partner AfriSam ensured fast track construction, facilitated by optimising early concrete strength and rapid cycle times.

The structure of 5 Parks Boulevard comprises conventional reinforced concrete slabs from the basements to the roof, with a lift core to accommodate three lifts down to the lowest basement. Built on four platforms with 80 piles, the building comprises four basement levels and five office levels – providing about 7,300 m² of gross leasable area (GLA).

Efficiency and innovation allowed the concrete structure – comprising 8,500 m³ of concrete – to be completed in just six months.

How the owner’s requirement was met

The client required a fast track performance from the contractor to meet the demanding deadline for tenant occupation. This had to be achieved while overcoming several technical challenges.

The project was required to form an extension of the greater super basement of Oxford Parks. The basement structure tucks into an elevated roadway (Parks Boulevard) which is constructed with cantilevers from the Phase 1 basement. The basement driveway circulates below the existing cantilever, requiring the roof of the building’s basement (which is to say, the ground floor) to be cantilevered by 1,5 grids (about 10 metres) to close off the basement. This was achieved with post-tensioned beams.

Other constraints included the limited headroom resulting from the road construction and the servitude above the basement slab.

To achieve the fast track schedule, a higher strength concrete (35 MPa) was used on the upper two floor slabs. This delivered a higher early strength, allowing Concor to strip its back-propping earlier and complete the facades, finishes and services inside the top two levels – paving the way for beneficial occupation. Tenants required a weather-proof building before they could begin their six month beneficial occupation period.

Concrete as the solution

Concrete is still the most reliable, cost effective and robust material for constructing commercial buildings in South Africa. With AfriSam’s leading position in developing low carbon cement and concrete, these buildings can be constructed not only cost effectively but also in line with Green Building principles.

Nature of concrete

The readymix concrete for 5 Parks Boulevard was supplied by AfriSam’s Wynberg Plant near Sandton. Most of the concrete used in the project was a Green Star 30 MPa mix, which was used extensively on the surface beds and slabs. Aggregates were produced from granite material at AfriSam’s Jukskei Quarry in Midrand, where the blend of fine and coarse material was optimised for the application.

The cement used in the concrete mix was an AfriSam High Strength Cement (HSC) which also incorporates clinker replacement, giving it a low carbon footprint while retaining its high strength performance. The cement is factory-blended with fly ash, up to 11 to 12% in content.

Bespoke admixtures were sourced from CHRYSO Southern Africa and included a mid-range water reducer specially designed to enhance the performance characteristics of the AfriSam cement with the appropriate lignosulphonate and polymer components.

Slabs and verticals

Each level of slab consumed between 150 m³ and 250 m³ of 25 MPa readymix concrete, with the bulk supply of all readymix concrete provided by AfriSam. The slab on each level was placed in four pours, with the schedule requiring on average two pours per week.

While 25 MPa and 30 MPa strength concrete was usually used for the slabs, higher strengths from 35 MPa to 60 MPa was used for the columns and verticals. This enabled cycle times to be accelerated as the slabs could be de-stressed and formwork recycled to the next level more quickly saving time.

Pumping and placement

Most of the concrete for the slabs was pumped using mobile pumps, while the concrete for vertical elements was placed using a tower crane.

Ingenuity and innovative methodology

Hydraulic shaft formwork system

In addition to special mix designs, the hydraulic self-climber methodology used for the vertical lift core construction reduced overall cycle times from the conventional 11 days to nine days for horizontal slab construction.

Space on the site was very constrained, so a tower crane was used to facilitate the quick pace of construction, moving material for the wet trades and other functions including the placement of plant on the upper levels as the building progressed. The hydraulic self-climbers played an important role in freeing up the crane to conduct other important and urgent work necessary to meet the demanding schedule.

Cantilever with bonded post-tensioning

As mentioned above (in section on ‘How the owner’s requirement was met’), the innovation in this project included a one-and-a-half grid cantilever with bonded post-tensioning in the beams under the road slab. Concor was able to modify the road’s cantilever beams to create the increased headroom necessary for vehicle access.

This required back-propping of the road while it was in use, the cutting of cantilever beams to the required headroom height and reinforcement with structural steel beams and plates. This was bonded with epoxy onto the cantilever beams to strengthen the structure – before the back-propping could be removed.

Normally, a roof over a basement is the transfer level, requiring the basement to be capped with a straightforward slab-column grid. To accommodate the top structure, there is normally an elaborate structure of transfer beams; the series of concrete pours necessary would have risked time over-runs on the project’s tight schedule.

Working closely with the designers, Concor developed a solution that suited the shorter timeframe in the programme for those elements. With the use of post-tensioned cantilever beams, the structural engineer was able to avoid the use of too many transfer beams, steps and other elements that would have been time consuming.

Premanufactured facades

Another important example of quality coupled with time savings was the premanufacturing of the façade panels. This was made possible through accurate detailing at the start of construction and it is noteworthy that the tolerances achieved with the concrete structure were such that the premanufactured panels were installed with precision.

Quality assurance and testing

Quality assurance played a pivotal role on the project with the added benefit of the cohesive and experienced team ensuring continuous quality assessments and control which considerably reduced the amount of snagging at the end of the project. The approach was applied to all trades and when it came to the readymix concrete, Concor conducted its own cube tests through an external company after every concrete pour. This was in addition to the testing done by AfriSam.

The consistency of concrete strengths at each interval – which aligned with South African National Standards (SANS) – was an important part of maintaining the fast track construction programme. Concor made use of an independent facility, Concrete Testing Services, for the regular testing of its concrete mixes. Tests were conducted on a four day, seven day, 14 day and 28 day basis. Quality assurance and trend analysis was carried out. No issues were identified with any of the mix designs during this project. This assisted greatly in streamlining the planning and stripping process.

For the larger pours, tests were conducted daily for every 50 m³ of every mix – tracking four day cube results to ensure that the required early strip could be safely conducted. Excellent four day results were achieved with the AfriSam mix, allowing Concor to strip its back-propping earlier – opening up space for subsequent activities to start.

AfriSam applied its comprehensive testing regime of one in every 100 m³ supplied (since revised to one in every 75 m³ supplied). These are conducted on a random basis, targeting the larger pours to achieve representative samples of what is supplied throughout the day. Test cubes were made every seven days and 28 days. Mobile laboratory technicians executed a testing programme which was compiled specifically to suit the daily sales schedule.

Cubes were sampled on-site, tying the sample to specific batch reports. This allowed the materials that went into a specific load to be linked to the results of that sample. All samples were statistically analysed so that trends were identified at an early stage, and any necessary action taken timeously. All the information generated from this process was made available to the customer.

Innovating sustainability into concrete

As mentioned above, 5 Parks Boulevard qualified as a Green Star rated building. Among the factors considered in this rating, the concrete mix designs used in the construction had to contribute to reducing the overall carbon footprint of the structure. This was achieved by using more fly ash in the mixes reducing cement levels by 30%. Less cement means less clinker, which consumes considerable energy in its manufacture.

Water stewardship is an important aspect of the sustainability commitment at AfriSam’s Jukskei Quarry which supplied the readymix for 5 Parks Boulevard. Water used for the cleaning of the readymix trucks is recycled. After it is used in the washing process, it is channeled to settling pits to settle out the solids. This allows water from those pits to be drawn out again and used in the cleaning process. The water used for the concrete mixes, however, is of a potable quality to ensure the required performance.

Sourcing the readymix from nearby plants assisted the project to limit its carbon footprint. With the AfriSam quarry just 15 km from the building site, the carbon emissions of the readymix trucks could be kept to a minimum. The cement was sourced from AfriSam’s nearby Roodepoort plant – a distance of some 30 km away. The limited distance travelled by the materials for the concrete allowed it to be well rated in terms of the Green Star system.

Balancing sustainability and risk

AfriSam’s commitment to sustainability was delivered alongside strong risk mitigation strategies, based on the proximity to site of both its Wynberg and Jukskei facilities. The 80 m³ supply capacity of the two plants at Wynberg is matched by a similar capacity from the two plants at Jukskei – providing adequate support in the event of an unscheduled stoppage. Using the same material (from Jukskei Quarry), the two facilities could assure the customer of seamless delivery.

The demand requirement of the project averaged 400 m³ to meet the fast track schedule; the concrete structure represented the critical path through the building programme, so reliability of readymix supply was vital to success.

This factor became even more important when the project encountered an extended period of intense rainfall, which threatened to cause delays. In response, the project team made up time during the concrete framework phase, which was made possible by reliable and punctual readymix deliveries from the nearby plant.

Green Star achievement

The alignment of 5 Parks Boulevard with the Green Star rating framework of the Green Buildings Council South Africa (GBCSA) demands compliance not only in terms of the design and operation of the building – but also the construction process. Concor’s strict performance strategies to manage water use, energy consumption, process waste and pollution all contribute to upholding critical environmental standards. In addition to carefully applying the client’s sustainable designs, Concor’s quality systems therefore all contribute to the points requirement in the GBCSA rating.

Concor’s ISO 14001 environmental certification also required that the project’s suppliers and subcontractors be sourced within 40 km of the site, where possible, to reduce the carbon dioxide footprint. In compliance with the Green Star rating criteria, the building process is conducted within the confines of an environmental management plan and waste management plan. All waste is separated into wood, steel, cementitious and general waste on site, and placed into the appropriate skip containers before being removed and disposed of responsibly by certified waste removal subcontractors.

The green design of 5 Parks Boulevard includes photovoltaic panels on the roof, which will generate renewable energy for up to 90% of the tenants’ needs. As part of its energy efficient design, the building incorporates an air cooled chiller plant which is a closed system that reduces water consumption. To further support the energy efficiency requirements of the Green Star rating, the building makes extensive use of glass windows – about half of which are double-glazed. Thin-glazed glass was mainly used on the atrium side, with punch windows being installed for the rest of the building.

Investing in skills and communities

Supplier development

The development of small, micro- and medium-sized enterprises (SMMEs) in the supply chain was a key focus on the 5 Parks Boulevard contract, as it is with all Concor’s construction activities. Concor works with subcontractors to ensure they not only deliver quality performance but also to assist them in honing their business and technical skills. This approach raises the game of subcontractors and makes them inherently more sustainable, while not compromising the broader project in any way.

Building future skills base

Concor proactively invests in the development of graduates within the building and construction sector – on a number of levels – and 5 Parks Boulevard provided a valuable learning platform for young graduates and students to build their skills for a productive future in the industry.

Firstly, the company operates the Concor Graduate Development Programme, through which young graduates were given full time employment on the 5 Parks Boulevard project. Assigned to roles in accordance with their training to date, they were able to gain vital experiential learning on site, while receiving mentoring and valuable site exposure.

Students in courses such as construction management, quantity surveying and safety management were given the opportunity to do vacation work as part of the 5 Parks Boulevard team. Here, they received valuable work experience – which was also a pre-requisite for completing the courses on which they have embarked. They are also mentored and coached by experienced staff on site ensuring that they can practically apply their theoretical training in a way that is safe and constructive.

On this specific project, a junior quantity surveyor was employed from within the local community as part of Concor’s commitment to uplifting and skilling people in the vicinity of the project.

Doing good in communities

Nearby the Rosebank project site is the St Vincent’s School for the Deaf and the company was responsible for managing the renovations to their kitchen facilities as well as their coffee shop. The company also assisted in the clean-up drive in the area surrounding Oxford Park as part of its corporate responsibility to ensure a clean and safe precinct for the community. In a further initiative, Concor has a longstanding relationship with the Bramley Children’s Home and provides financial support.

Managing risk

Risk management plays an important role on all Concor’s projects, and it was no different at 5 Parks Boulevard. Careful attention was paid to the construction programme ensuring that the supply of materials would dovetail accurately with the programme’s daily requirements.

The fast paced nature of the project also necessitated dealing efficiently with challenges as they arose to ensure that these would not negatively impact the programme.

While the construction site itself was hoarded to isolate the working areas, the building was being constructed within a live precinct. This meant that due care had to be taken with all activities and especially when construction materials were being delivered to site. Being adjacent to buildings with other tenants also curtailed the working hours available to the team, particularly when noisy work had to be done.

Careful selection of subcontractors and suppliers was based, wherever possible, on their previous performance and track record. This ensured that both the supply chain and execution was streamlined to mitigate any risk in this area. The majority of SMME subcontractors on this project had previously worked within Oxford Parks and were also selected based on Concor’s previous experience with them.

Keeping it safe

Zero Harm was the watchword at 5 Parks Boulevard and this was achieved as Concor recorded a Zero Lost Time Injury (LTI) rate after more than 250 000 hours having been worked on the project. This was noteworthy both for the numbers of people on site and the pace at which work was conducted.

The compact professional team on this project successfully managed a large total headcount on site that rose to about 400 at peak times. At the same time it was a fast track programme on an extremely constrained site, located within an established suburban area bordered by commercial and retail developments. It is also worth noting that, despite the fast track schedule and weather-related delays, there was seldom any overtime worked to bring the project to completion on time.

Such was the significance of the safety performance that the project secured second place in the Master Builders South Africa (MBSA) Gauteng region Annual Safety Awards 2022 in its value category. In addition, it also earned a Five Star Grading from the MBSA.

One of the important factors ensuring this level of safety is that Concor has been involved for several years at Oxford Parks. This has meant that its own team, as well as the professional team, the subcontractors and the client have become very familiar with the working environment and strict health and safety standards. The teams and subcontractors on 5 Park Boulevard were therefore very clear about what was required of them – and worked cooperatively to coordinate their activities effectively and make quality and safety systems second nature. The constructive collaboration with the client’s team of consultants was also essential to success.