Offering a workable alternative to traditional concrete foundations, concrete garden pavers, outdoor entertainment areas, seamless driveways and garage flooring, find out how to fit concrete slabs as a DIY project at home.
The beauty of concrete slabs is they can be poured and placed in just about any shape, colour or surface texture imaginable as long as the form fits the function, what's more, placed on well prepared and compacted sub-grade, concrete slabs offer lasting durability at a fraction of the price compared to painstakingly mapping the route of intricate foundations, outdoor entertainment areas, patios and pavers.
The key to pouring a concrete slab lies in the preparation of the subgrade, where preventing cracks and fissures depends on the base the concrete settles on and how well the slab is protected from moisture absorption. Concrete slabs can be further reinforced using vapour barriers and a combination of rebar, wire-mesh or even fibre-mesh for added durability and load bearing capacity.
Placing concrete slabs at home can be a fairly simple process to follow with the devil in the detail of preparing a balanced, primed and well compacted subgrade. Together with a crushed gravel base to prevent natural sinkage from weight and added pressure and further reinforced by a level and compressed soil subgrade, concrete slab foundations and flooring will refrain from sinking or cracking even under the most extreme South African weather conditions.
Creating a concrete slab for beginners starts with the assembly of a sturdy timber frame to define the perimeter of the concrete base. Once enclosed around a well-prepared and compacted subgrade that has been finished with stone gravel, the gravel acts not only as an added layer of reinforcement on top of the subgrade but also as an effective filter preventing groundwater runoff and causing moisture to move away from the concrete slab.
Before pouring your wet concrete into place, wet subgrade slightly to avoid sucking the water out of the concrete, secure wire mesh or rebar inside your shuttered area ensure that the reinforcing is not laying on the gravel surface by lifting it to approximately centre of the slab using some bigger stones or commercially available spacers, which acts as concrete slab reinforcement, effective in increasing the load bearing capacity especially in frequent and weighty traffic zones such as driveways and garage flooring. Another detail to consider when pouring wet concrete to form a concrete slab is to do so at a very slight and gradual slope which will help water or moisture build up to run off instead of pooling in one focused depression in the slab.
Strategically beginning at the highest point of the slope, carefully pour and screed concrete into the timber frame and using a screeding tool flatten the wet concrete by sweeping the mix back and forth to create a uniform surface. Moving from the top of the slope to the bottom, create a flattened concrete surface that can then be compressed using a floating device to press aggregate gravel beneath the visible surface while offering a smoothed out and creamy finish.
Next, make use of a groover to insert measured control joints every 2 meters which will ensure the concrete slab is able to endure thermal expansion and contraction and control the position of cracks to be directed to the predetermined joints as opposed to unplanned and unsightly random cracks. (The rule of thumb is that slab sizes do not exceed the following size. Slab size must be preferably less than 32 X Thickness of slab. E.g. if you intend to cast a slab with a 100mm nominal thickness the slab / block sixe should not exceed 100 X 32 = 3.2 meters)
For outdoor concrete slab installations keep in mind that surfaces will become slippery underfoot and adding traction is considered best practice especially when surrounding wet surfaces such as pool decks, outdoor entertainment areas and garden walkways. Traction can be easily created by simply using a stiff bristle brush to sweep gentle grooves onto the smoothed surface of concrete slabs. Alternative options include incorporating decorative stamping or finishing cured concrete surfaces with a grit sealant.
Whether you have a large or small concrete surface area to clean, removing dirt, grime and debris from concrete surfaces at home can be done quite professionally by applying a few basic care principles.
Indoor and outdoor concrete surfaces can be successfully cleaned without the help of professional cleaners with a few household supplies most of us already have available at home, but there is a place for professional cleaners as well, especially when concrete surfaces are largely soiled or have not been cleaned over a long period of time, the long term build-up of dirt, stains and marks caused by grease may need the help of a professional to get these cleaned.
It's also important to keep in mind that concrete is caustic and susceptive to corrosion and damage caused by compounds that trigger a chemical response. When cleaning concrete surfaces finished with epoxy coatings, colour stains, sealants or polished concrete floors make sure to clean these with a PH neutral detergent to avoid damage to these decorative surfaces.
Cleaning concrete surfaces without any professional supplies
Whether you are trying to remove, oil, grease marks or organic matter from indoor and outdoor concrete surfaces, large or small concrete surfaces, including those treated with a PH sensitive finish, can be cleaned safely by using a mix of dishwashing liquid and warm water. Creating a warm soapy mix of 30 millilitres of dishwashing detergent with 20 litres of water and gently scrubbing the surface with a soft bristle brush (or a broom for larger surfaces areas) is an effective way to remove every day dirt and trivial stains and grease mark from porous concrete surfaces. As the soap and warm water re-emulsifies oil-based marks, the surface can then be rinsed clear with clean and untreated water.
Cleaning concrete surfaces with a stronger home solution
It's important to note that using an acid or alkaline cleaning solution may provide a more effective result, however, these can corrode, discolour and peel decorative concrete surfaces, epoxy coatings and coloured stains and polishes.
While there are many natural solutions to cleaning concrete surfaces, these may not always be PH neutral.
For example, mixing 1 part vinegar to 1 part of warm water, or 10 millilitres of lemon juice to 1 litre of water makes for a stronger cleaning solution, both vinegar or lemon juice (in its natural state) are high acid cleaning solutions perfectly fine to be used on untreated concrete, but should be avoided when cleaning decorative concrete surfaces.
Another home solution stronger than dishwashing liquid and water is a solution made of 1 cup of bleach and 2 cups of bicarbonate of soda mixed in 20 litres of water (for very stubborn oily stains a 10ml Ammoniac can be added to this solution and then care must be taken not to inhale the fumes – cover nose and mouth with a wet cloth). Especially useful in removing mould and mildew, this solution has a high alkalinity and will have an equally damaging effect on surface treated concrete in the same way as high acid cleaners do. If cleaning surfaces from oil where it is not going to matter if there is a colour change, white spirits can be used (white spirits tend to leave white stains/marks on concrete).
Alternative cleaning methods that are effective and require the least amount of manual labour include the use of high-pressure washers for outdoor surfaces or steam cleaning machines for indoor and decorative surfaces, where both are pet friendly, non-toxic cleaning methods that are especially useful on larger surfaces.
While a common assumption that pouring concrete in wet/rainy weather presents more favourable curing conditions, see Sephaku Cements top tips and tricks to pouring concrete in rainy climates making sure your concrete pouring project is a solid success.
As one of South Africa’s provinces moves from a hot and wet summer, another one of our provinces are lined up for a cold and rainy winter which means inevitably South African concrete contractors will all be required to pour concrete in wet and rainy conditions at some time during the year. While concrete and water go together like a hand in glove, there are very specific guidelines that should be followed under wet and rainy conditions to make sure the integrity of your concrete project is not compromised by unpredictable summer thundershowers or weeklong soft soaking rains. As with so many things in the concrete construction business, success is largely put down to the timing of things, whereby with planning and a little bit of forethought, even the most disastrous conditions need not stop your progress.
Plan Around Weather Forecasts
While it’s neither a fool-proof method nor wise to place all of your faith in the weather forecast, a good place to start is by planning your concrete pouring project around expert weather predictions. With a number of resources that offer a near accurate seven to ten-day weather forecast begin by keeping a close watch on the coming weather predictions planning your project around the drier days than on the scheduled wet ones. No matter how much pressure your project may be under, it’s always a smarter choice to postpone pouring until drier conditions if the weather forecast predicts wet/rainy weather.
In the case of an unpredictable summer thunderstorm, hard and fast rain can negatively affect newly poured concrete, causing the surface to become over saturated and soft, compromising the overall strength and increasing the risk of cracking once cured. If your concrete project has been poured within a few hours of a fast-moving thunderstorm try to protect the surface of the concrete by erecting a temporary shelter above the worksite even if this is effective enough to deter just some of the downpour.
Sweep Away the Excess
Once a sudden downpour has come to an end, never try to blend excess rainwater into poured concrete, remember that the correct water to cement ratio must be adhered to in order to ensure the concrete cures with its required strength. Provided that doing so won’t damage or deface the desired finish, try to push or pull excess water from the surface of recently poured concrete. If the concrete was placed between four and eight hours prior the rain setting in, you need not be concerned with removing any excess water from the surface.
Pouring Concrete After the Rain
While waiting for the rain to subside before placing new wet concrete, it’s important to note that wet concrete should never be poured into a hollow filled with water or cavities and groves that are filled with remaining water or runoff. By doing so, much in the same way as rain falling and pooling onto the surface of concrete, concrete poured into a puddle of rainwater will adversely affect the water to cement ratio compromising the strength and consistent curing of your concrete project.
While concrete contractors can on the most part operate all year round, as seasons change bringing about varying weather conditions, see Sephaku Cement’s top tips and guidelines on seasonal concrete pouring.
Known for its warm and mostly sunny days, South Africa’s weather ranges between Mediterranean to Subtropical climates where conditions are typically influenced by the differences in the county's varying
landscapes. While conditions are rarely extreme, temperatures are known to plummet a few degrees below freezing in winter, both summer and winter rains are encountered depending on the region you are working in and high summer temperatures can see the mercury rise in close vicinity and in some provinces even over the 40°C mark.
Variations in the weather bring about varying ambient conditions that can influence the pouring and curing of Portland cement concrete to follow see guidelines for curing concrete in different South African seasons.
Pouring concrete during a scorching African Summer
South Africa Summer temperatures are usually above 32°C countrywide and, in some regions, often peaking up to 38 °C, temperatures, humidity and wind factors will each play their role in influencing the rate and consistency of how wet concrete cures. While Portland cement concrete is not particularly fussy when it comes to weather conditions, careful attention needs to be paid to keeping the curing speed and process consistent.
Where temperatures climb above 32°C concrete contractors need to take care that the surface of poured concrete are kept cool. To do this, begin by making sure that the materials you are using are kept
in a cool place or could be kept cool with a fine mist sprayer whereby for example if aggregate sand and stone has been left to bake in the sun, this will just add to the rise of the concrete temperature above 32°C. Another tip when mixing concrete in hot conditions is to make use of cold water (some contractors often especially when pouring mass concrete like dams where heat of hydration contribute to internal concrete temperatures, even go as far as using ice as a water substitute) and once poured into
place keep the concrete surface moist by lightly watering it with the sprinkler or a fine mist.
Pouring concrete under cold conditions
While daytime winter temperatures in South Africa rarely reach below freezing, night-time temperatures in the dead of winter can often plummet into negative numbers on the thermometer. Concrete cures at a slower rate in cooler temperatures which, if kept above freezing are favourable conditions for optimal curing. However, if the ambient temperature reaches below freezing the risk is that the water in wet concrete may freeze before it cures. When water freezes it expands which will result in larger pockets in between the already porous structure of cured concrete and could potentially even crack concrete if it has not reached at least 5-10 MPa. So what’s the issue you may ask? If allowed to freeze, pouring concrete in below 5°C and falling freezing temperature will increase the risk of cracks and fissures as a result of the freezing water in the concrete. To keep curing concrete from freezing in winter begin with mixing combined materials with warm water and conversely to summer tips, let stone and sand aggregates sit in the sun if any, to increase the ambient temperatures as much as possible. Plan concrete pours to take place early as possible to allow strength of 5-10 MPa to be reached before temperatures fall below zero°C. Most contractors will also leave shutters on and insulate the open surfaces with polystyrene when casting mass concrete in the winter to prevent the temperature differential between inside and the concrete surface to go beyond the allowed 17°C. Another tip is to make use of early strength cement that has been blended with various additives to influence the strength class and strength gain pattern of the concrete. Using products such as Sephaku 32,5R or Sephaku 42,5R where the R denotes rapid strength gain Portland cement means that the cement has been engineered to deliver an improved early strength and rapid curing.
One of the leading causes for major structural damage to homes, schools and places of business, learn to identify tell-tale signs of distressed foundations, what is causing this to happen and the risks associated to damaged concrete foundations.
Much in the same as a chain is only as strong as its weakest link, structures and standalone fittings such as boundary walls and other applications placed on concrete foundations, are only as steadfast as the foundations they are built on.
While water or ongoing exposure to moisture is typically the primary cause of damage to any concrete installation, there are a few other factors that have a hand in causing damage to concrete foundations that include;
Subgrade Soil Type and Preparation
Typically clay type soil is guilty of becoming expansive both by swelling and contracting depending on the water content present. Comparatively sand type soil can lose traction and sift with time creating an equally unstable surface for long term foundations. While soil type should always be a consideration for sound foundations, so should the preparation of the foundation’s subgrade. Using an infill material from a good quarry is an alternative if insitue material is not sufficiently stable for a proper foundation, subgrade should also be effectively compacted to prepare a stable and compressed surface on which to place steadfast foundations.
Improper water drainage
Pooling in and around foundations, if rain water or irrigation run off is not adequality drained away from foundations, ongoing exposure to water that is absorbed into the air chambers of concrete will freeze and expand, thaw and retract forcing the concrete to become brittle and distressed over time.(not common in South Africa except can occur in very cold/high altitude places like Lesotho)
Extreme Weather Conditions including floods or droughts
Also influenced by the presence of water or moisture in the concrete matrix, extreme weather can have a negative impact on concrete. Whether too much moisture, freezing temperatures of extreme heat and dry spells that can evaporate moisture, each of these conditions eventually erode concrete foundations.
In areas of increased seismic conditions, earthquakes can wreak havoc on concrete foundations as the surface of the earth shifts, shudders, rolls and shakes concrete installations during an episode. Damage is not only cause by movement originating from beneath the surface of the earth, but the shift in pressure of the construction on top of the foundations.
Surrounding Influences such as tree roots and other subgrade disruptions (like big boulders in surrounding soft sandy soil).
Exerting pressure on surrounding soil or directly intruding on concrete foundations, the roots of large trees are known to cause some significant damage to concrete foundations. Leaching moisture from soil and subgrade, uprooting slabs and even bursting underground water pipes flooding foundations, tree roots should always be a consideration when planting to nearby construction. (best to involve a horticulturist)
Regardless of the cause, damaged concrete foundations compromise the integrity of the structure in question while also having a negative impact on the property’s value and cause unsightly blemishes like cracks and surface warping even requiring to demolish buildings with severe foundation damage, to name a few.
So, what are tell-tale signs that your foundations are damaged or in need of repairs?
While all new construction settles into place with time, if foundations are insecure and of not sufficient size or strength and under duress, there are very apparent signs to tell foundation issues apart from slight and organic shifts.
The most obvious signals that foundations are unstable are;
- Cracked bricks
- Misaligned doors and windows
- Cracked or uneven floors
- Wall rotation or leaning – off plumb
- Splits in masonry where brick separate form mortar
An alarming amount of homes and other structures are built on inappropriate subgrade and damaged foundations that can cause costly structural damage and more concerning compromise the structural integrity making the building a hazard and unsafe to occupy.
While hairline cracks in concrete foundations are normal and mostly unavoidable given the effect of freeze thaw expansion and contraction when exposed to water or moisture, experts estimate that if a crack is broader than around 3 mm, this could be a good indication that concrete foundations are in need of a foundation inspection and repairs by a foundation specialist. Foundation repairs are extremely difficult and not always successful, besides it being very expensive.
With early detection and effective repairs made to damaged and distressed foundations is one of the surest ways to prevent lasting and hazardous structural damage to your home/building. Often when left too late damaged foundations negatively impact the structural integrity of buildings that are too far gone to be repaired. Requiring a comprehensive rebuild from the ground up, leaving damage foundations to literally tear through any structure is not only costly but dangerous for occupants too.
Identifying damaged foundations can be done by a simple inspection of the foundations or by looking for tell-tale signs of damage to structures that may indicate distressed foundations. Structural engineers as well as a foundation repair expert will also be able to assess your property and note any concerns that should be addressed to prevent structural damage before it’s too late.
Once it has been identified that a structures foundation is in need of repair there are a few methods in which structural engineers and foundation repair specialists will approach the restoration of damaged foundations.
The most effective way to repair distressed and damaged concrete foundations is by blending the best in technologies and industry experience to apply effective solutions to damage foundation.
Today there are more effective and technologically advanced approaches to repairing foundations and where many contractors offer a lifetime guarantee on their repairs (subject to service provider).
Once having established the cause of foundation damage your structural engineer will be better advised to recommend an appropriate repair process typically being one of two methods, namely piering or slabjacking.
Just as the name suggests, slabjacking sees concrete grout used to lift a concrete slab or beam up towards a warped or shifted foundation taking on its original position. Typically used to repair sunken driveways and pavements, outdoor entertainment areas and patios, a simplified slabjacking technique can also be used by pouring concrete grout down boreholes, filling the gaps of compromised foundations with grout which then cures around the original foundation, reinforcing it from the bottom up.
Typically used to repair more extensive and significant damage to foundations, the piering method makes use of steel posts to stabilise or raise concrete foundations damaged by compromised subgrade and soil types. This method is effectively used in homes or commercial buildings and requires the opening of the damaged foundation by digging under and around it then a steel beam or posts are placed and with the help of a mechanical jack that is used to lift and secure the damaged foundation into place. Then an amount of concrete is placed around and under the damaged foundation. And left to set and gain strength.
From function to form, Portland cement can be put to task in a variety of ways and with some of the coolest uses and interesting facts that you may not have been aware of up until now. The most widely used building material in present day and with its foundations dating as far back as ancient roman concrete, cement is by far one of the coolest construction materials around given its hugely versatile and resourceful purposes.
Let’s take a look at the Top Five Things That Make Concrete Cool.
- Heat of Hydration
To the untrained eye it’s easy to assume that mixing Portland cement with water to form a paste is as simple as mixing flour with water to make glue. While the principle might be similar, you’d be mistaken to assume that there wasn’t a little bit of magic that happens as concrete creates some of the most magnificent and longest standing man-made forms in the world. The process of blending cement with water that then later cures is in fact a chemical reaction that occurs as compounds in the cement comes into contact with water. What happens next is in fact rather astounding whereby wet cement starts heating up, this process is referred to as the Heat of Hydration which sees to it that large bodies of wet cement can emit a fair temperature increase as it hydrate, set and cures.(up to 70OC in certain cases of mass concrete)
Built to last a lifetime and more
With an astounding compressive strength, it’s no surprise that some of the oldest standing constructs were originally made from earlier forms of concrete. Known as the largest unreinforced concrete dome said to have been made from a blend of lime and volcanic ash from Mount Vesuvius erected in 126AD, the Pantheon is an excellent reminder of just how steadfast and durable concrete can be. Another impressive example and a little closer to home; the Western Cape’s Castle of Good Hope is known as the oldest colonial building in South Africa and one of the world’s best preserved examples of the Dutch East India Company’s 17th century architecture. Built between 1666 and 1679 it has been explained that the cement used to erect this historic landmark was made by burning shells in lime kilns until it formed lime which was then once again mixed with shells and sand to create a concrete.
As big as it is heavy
Some of the world’s largest and heaviest structures have been built using concrete including the Three Gorges Dam in China weighing in as the heaviest concrete structure in the world at a weight of 144,309,356,753.51 pounds. The amount of material used in the building of the Three Gorges Project is staggering. Consuming 28 million cubic meters of concrete. The Three Gorges Dam is the world's largest capacity hydroelectric power station with 34 generators: 32 main generators, each with a capacity of 700 MW, and two plant power generators, each with capacity of 50 MW, making a total capacity of 22,500 MW. Meanwhile the Empire State Building in New York, United states, was built using 62,000 cubic yards of concrete and was known as the world’s tallest building until the rise of the Burj Khalifa in Dubai 2010. At over 828 metres (2,716.5 feet) and more than 160 stories, Burj Khalifa holds the following records: Tallest building in the world. Tallest free-standing structure in the world. Highest number of stories in the world. Locally the Carlton Centre a 50 storey skyscraper in downtown Johannesburg was formerly known as Africa’s tallest building but has since relinquished its title to the 55 reinforced concrete floors of the Leonardo Hotel in Sandton Johannesburg.
The most widely employed material in construction world-wide.
It’s a concrete fact that cement is the most commonly used material across the globe. After the Washington Post estimated that China’s use of concrete between the period of 2011 and 2013 exceeded the USA’s use of this popular building material throughout the entire 100 years of the 20th century, it has since been predicted that the global demand for cement will increase by almost 5% year on year calculating that the construction industry will have consumed some 4.2 billion tons of cement in 2019
(Back in 1995, the total global production of cement amounted to just 1.39 billion tons, which indicates the extent to which the construction industry and therefore the consumption of cement has grown since then.)
Concrete 3D Printing
What was once largely limited to the use of molten plastic and metal, 3D Printing technology has evolved to now employ the use of wet cement blends. Revolutionising the architecture and construction industry in leaps and bounds, concrete 3D printing technology offers an efficient and cost effective alternative in basic construction. Using a method similar to fused deposition modelling (FDM), concrete 3D printing takes place using an automated and repetitive methodology that directs a print head through a sequence of rotations. While designs may still be limited to more modest forms, concrete 3D printing can be extremely effective in the construction of high density, low cost housing in areas of high demand.
From historic concrete landmarks to more modern constructs, see how concrete has been shaping South Africa’s landscape for centuries gone by. A material so durable that today it is one of the most widely used building materials in construction, using a blend of Portland cement, various textured aggregate and water, join us as we explore various concrete constructs that line South African horizons.
- The Castle of Good Hope - Cape Town
Set against the backdrop of the Table Mountain in the Cape Town CBD the Castle of Good Hope was erected by the Dutch East India Company between 1666 and 1679 and is said to be the oldest colonial building in South Africa still standing today. Building materials used to construct this historic monument included cement created from burning shells in lime kilns which was then blended with crushed shells and sand to a durable concrete.
- Table Mountain Cable Way – Cape Town
An engineering project that saw construction workers having to carry equipment and materials to the top of the mountain before construction could begin, the Cape Town cable way took four years to build and was first opened in 1929. Making use of a temporary ropeway and an open box called the " Soapbox" to carry cement and other building materials as well as workers up and down the mountain, surprisingly the Table Mountain Aerial Cableway has remained accident free for more than 90 years.
- Orlando Towers – Johannesburg
Completed in 1951 The Orlando Towers were originally built as part of a coal fired power station which took 20 years to build due to delays attributed to World War II. Decommissioned in 1998 the towers are today a defining landmark in Soweto where both concrete constructs stand 33 storeys tall, painted with images of township culture and welcome an abundance of local and international tourists to extreme sporting and cultural attractions.
- Ponte Tower – Johannesburg
Still the tallest residential apartment building in Africa, Ponte Tower was completed in 1957 standing 54 storeys and 173 meters high. A recognisable landmark against the infamous Johannesburg CBD skyline, Ponte Tower is a reinforced concrete tube complete with an open-air centre that was originally intended to allow more light into the cylindrical construct.
- Concrete Dolos - East London
Designed by a world famous South African harbour draughtsman Aubrey Kruger, the dolos sea buffer system of interlocking concrete is still used today to dissipate waves at rough breakwaters all around the world. Having based the design on the dubbeltjie thorn (Devils Thorn), original dolosse were cast into unreinforced geometric concrete designs weighing up to 20 tons per piece and placed in an interlocking matrix. Extremely effective in reducing the force of breakwater waves these designs are still used today some 50 years after conceptualisation.
- The Administration Buildings of UNISA – Pretoria
Known to many as "Die Skip" (the Ship) the Administration Building of the University of Pretoria UNISA makes for a striking backdrop when entering the capital city of Pretoria. The three-pointed star shaped building was completed in 1968 but later expanded to accommodate for more office space and features a magnificent concrete facade on the northwest wall adding texture and drama to the already commanding concrete construct.
Using a general purpose, normal strength cement such as Sephaku 32,5N or Sephaku 42,5N for the more serious builder, Sephaku Cement shares a step by step process on how to make DIY concrete bricks.
The most commonly used material in both the formal and informal construction industry; Portland Cement, offers the industry a durable and longer lasting building solution to any other material used in foundations, mortar, paving, roofing and flooring. Historically bricks were more commonly made from clay and clay derivatives, but making use of concrete bricks was a means to more cost effective masonry work, concrete bricks are now widely used in construction depending on the desired finish.
To follow, see how to make your own concrete bricks using Sephaku Cement with these simple steps.
- Step One: Preparing a Timber Casting Mould
With the help of a very simple wooden framework making your own concrete bricks is a walk in the park. With this step being as complicated as its going to get, using timber boards measured and cut to size together with a plywood backing reinforced by plastic sheeting to prevent leaking, nail together a wooden casting mould used to shape your concrete bricks into the appropriate dimensions.
While you can create a casting mould and bricks as large or small as you’d prefer, the following specifications are measured to make a mould that will result in a batch of eight cement bricks at a time, each measuring dimensions of
5.1cm wide, 22,9cm long and 8.9cm deep.
Erect your timber casting mould that will resemble that of a wooden ladder with equidistant steps and a plywood backing by measuring your timber with two sides of 1.2 m long and nine “steps” measuring 22.9 cm in length, spaced 5.1cm (4 inches) apart.
Using plastic sheeting as a backing, place your stepladder framework on the plywood backing which will help prevent the wet concrete from oozing through the cracks/joints once poured into the frame. It’s also recommended that you spray each mould with an aerosol lubricant or oil to assist in the removal of the bricks once cured.
- Step Two: Mixing Brick Cement
Making use of a normal strength cement such as Sephaku 32,5N or Sephaku 42,5N, begin by blending the cement together with a mixture of coarse and fine river sand aggregate measured at typical rations of cement to sand mixtures of 1:7, 1:8 or 1:9. Before mixing with water blend together the dry ingredients ensuring that the aggregate and cement is completely combined. Next create a well in the centre of the concrete blend and following the applicable water rations detailed on the bag of cement, very slowly add water to the mix to wet the mixture little by little as to not over wet the mixture. The mixture must be dry but not crumbly.(able to be easily squeezed into a ball)
- Step Three: Pouring and Curing Cement
Carefully fill your timber mould with wet concrete doing so more effectively using a spade instead of pouring it into the cast. Pay careful attention in making sure that the corners of each mould are filled or your bricks will not cure with perpendicular edges. Once each brick mould is filled gently tap all around the timber mould which will help to settle the concrete mixture into the corners. Using a straight edged trowel smooth out the surface of the concrete bricks levelling the surface as you go and then cover with a plastic sheet which will help to regulate the rate at which the brick cures during the first 24 hr period. The brick can be taken out of the mould very carefully and could be cured further after taking them out of the moulds by keeping them wet and covered with plastic sheeting. Once cured, The DIY brick can be used for your project.
As 3D printing, also known as additive manufacturing, continues to revolutionise a growing number of industries, Sephaku Cement explores how Concrete 3D printing is put to task in architecture and construction. Having already successfully created a number of prototypes and extremely technical products such as the intricate parts used in aerospace and aviation, as well as medical products including implants and artificial organs, 3D prints continues to pave the way as manufacturing and production marches into the 4th industrial revolution.
There are three common methods used in 3D printing technology, these include;
- Fused filament fabrication (FFF) or fused deposition modelling (FDM) which makes use of plastic materials that are heated and then pressed through a nozzle while following a pre-mapped design path
- Stereo-lithography (SLA) makes use of UV light to cure resin type materials one layer at a time
- Selective laser sintering (SLS) is more commonly used in industrial production and uses lasers to fuse powdered materials together one layer at a time.
From the design to the engineering and manufacturing, concrete 3D printing technology offers an efficient and cost effective alternative in the construction of a number of concrete applications. While initially limited to the use of molten plastic and metals, as 3D printing tech continues to advance, alternative materials are being employed including the likes of cement/concrete.
While concrete 3D printers are fairly significant in size especially for the construction industry, their mobility allows for basic concrete construction printing to occur almost anywhere and under various types of conditions.
Making use of a method similar to the Fused Filament Fabrication (FFF) or Fused Deposition Modelling (FDM) mentioned above, concrete 3D printing takes place using an automated and repetitive methodology that directs the print head through a sequence of rotations. While designs may still be a little basic and limited to more modest forms, concrete 3D printing can be extremely effective in the construction of high density, low cost housing in areas of high demand.
Basic Steps in the Concrete 3D Printing Process:
- As with any construction project, contractors begin by flattening the subgrade surfaces and placing sound foundations to work from.
- Once the foundations are in place, 3D printing technologists map the repetitive route that the 3D printer will follow using rail-like pathways that mimic the design. The 3D printer is then secured to the pathway rails and further guided by pillars for additional reinforcement.
- Once the design has been finalised and the printer’s route mapped out by the rails, a premixed concrete truck is connected to the 3D printer nozzle. The concrete mix used must be both fast curing as well as easy to pour, bonding to each layer as the concrete mix is pressed out of the printer. Making use of both superplasticizers as well as reinforcing fibres the ideal concrete mix can be achieved with the correct blend of chemicals and additives combined in the concrete
- The concrete 3D printer is now ready to begin following its repetitive path along the guiding rails depositing the exact amounts of concrete mix layer on layer.
With some concern that these concrete construction “bots” may eventually replace their human counterparts, concrete 3D technology is not without its shortfalls, although exciting technology is but only in its infancy, and will need much more development in future and will never fully replace the hand of construction contractors, workmen and architects.