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Concrete Technology 101
Date: 25.04.2021 Written by: Mr. Martin Gerard Joachim David Concrete is perhaps the most important construction material other than steel for the construction fraternity. It is easy to develop a specific type of concrete at the university laboratory but the story is vastly different when the same concrete is placed at the construction site in a bigger volume. So it is important to understand the different components of concrete and how the different components interact within the concrete mix. Traditionally, concrete is made of cement (Ordinary Portland Cement – OPC) + Water + Sand (Fine Aggregate) + granite stones (coarse Aggregate). For ready mix concrete, concrete admixtures such as retarder and superplasticiser are normally added to allow for transportation and maintain concrete specification. Cement (OPC) is the binder or the glue that bonds the fine and coarse aggregates together when both are mixed together. Water acts as the activator of the cement and help the transportation of the cement in a paste form around the aggregates so that a bond is created between the different ingredients inside the mix. The sand (fine aggregates) fills the voids in between stones (coarse aggregates). When the cement paste is set and given enough time to cure, concrete in its hardened state is formed. For the understanding of concrete enthusiasts, a basic design of concrete mixes is explained below: First of all, concrete that uses Ordinary Portland Cement (OPC) as the binder, can achieve a design strength of up to 60 N/mm². Beyond this, special additives will have to be added. Generally, concrete strength starts with grade 15 N/mm². For every increase of 5 N/mm², it is considered one grade higher. Now certain “Rule of Thumb” needs to be known and they are briefly explain as follow: - · 10kg/cement 1N/mm² · Water to cement ratio (WC ratio) not more than 0.5 (unless otherwise prescribed). · Approximately 20% of cement will not hydrate in the mix and will act as fillers. · Sand to stone ratio (SA ratio): 0.4 to 0.45 · 1m³ of concrete is about 2400 kg/m³ Assuming a Grade 30N/mm² concrete is required the calculation for the mix per m³ is as follows: - · Cement 30 x 10 = 300kg/m³ · Added 20% to compensate for the cement not hydrated. · Therefore cement content is 360 kg. · Water ( wc ratio) is 0.5 x 300kg = 150 kg/m³. · The cement and water weight are added to become 510 kg. · Since 1m3 of concrete weighs around 2400 kg, the weight of the stone + sand is 1,890 kg. · Now how much sand and how much stone to be used? · So we use the SA ratio of 0.45. We multiply 0.45 x 1890 kg (sand + stone) · Therefore sand will be 850.5 kg and stone will be 1039.5 kg. · In summary the theoretically grade 30 concrete mix will be Cement : 360 kg Water : 180 kg Sand : 850.5 kg Stone: 1039.5 kg Now we have to look at the basic admixtures which are retarders and superplasticiser. Without them, commercial supply would be impossible. Concrete without retarders start to set after 30 minutes once it is mixed and around 1½ to 2 hours for final set. This will make transportation and workability impossible unless the batching plant is located within the construction site. In most cases they are not. So retarders will have to be added into the concrete mix to prolong the initial set to approximately 2 hours and final set approximately 5 to 6 hours. The retarder works by lining the cement particles thereby not allowing the water to activate the cement. After the retarder time has become worn off, it will then allow the water to be in contact with cement and start the activation process. Keeping in mind that overdosing may cause issue with non-setting. The superplasticiser is mainly acting as a water reducer where by you can maintain workability without increasing water content and compromising on the strength of the concrete. How this works is that the superplasticiser lines the cement particles with a negative charge thereby repelling particles from each other, thus avoiding clumps and releasing trap water in the cement clumps. Water can be reduced by 25% approximately. In today’s technology, concrete is produced in automated or semi-automated batching plants. The pictures below give an idea on the production flow. Once the concrete is place, a poker vibrator is used to vibrate to compact the concrete and to release the air trapped inside the concrete. In order to work on the concrete, the concrete must not be too wet or too dry. In order to check the concrete before placing to ascertain the design slump which indicates it has been produce according to design specification. A slump check is done. To ensure that concrete has met its design, a compressive test is carried out 28 day after production. This article aims to provide a basic understanding of the concrete mixes. For more specific mix design, a more in depth understanding of concrete and others influencing factors are as important to achieve the intended outcomes. You may consult the professionals.
THE RELEVANCE OF TENSILE STRENGTH & ELONGATION OF WATERPROOFING MEMBRANES
Writer: Lee Chiew Fook (MAPEI Malaysia Sdn. Bhd.) Date: 13.03.2021 These properties are often headlined as important features of waterproofing membranes: a) tensile strength b) elongation at break How relevant are these properties for waterproofing performance? In order to answer these questions, it is necessary to first look at these definitions: Elastic Deformation and Elastic Limit An elastic material deforms when a force is applied to it. So long as the deformation stays within the elastic limit, the material will revert to its original shape when the force is removed. Many waterproofing materials which are described as elastic do not show perfect elastic behaviour i.e the recovery is not 100 % after the force is removed. Plastic Deformation A plastic material also deforms when a force is applied to it. However, when the force is removed the material will not recover its original shape. Many plastic materials used for waterproofing exhibit a small recovery but not enough to justify calling them elastic. Elastic materials which are stretched beyond the elastic limit but before the breaking point will deform plastically i.e. with little or no recovery. Young’s Modulus of Elasticity, E Young's modulus measures the stiffness of elastic materials or the force needed to deform an object along an axis when the force is applied along that axis; it is measured as the ratio of stress to strain (change in length over the original length). Comparing two materials with differing E values, the material with lower modulus requires less force to elongate it by a defined amount. In other words, and this is relevant for assessing waterproofing membranes, the material with higher modulus is stressed more for the same elongation compared to a lower modulus material. a) How important is the tensile strength? For fully-adhered membranes, consider the stresses imposed on it when the supporting substrate moves due to, for example, settlement or temperature changes. Under these circumstances, the membrane’s tensile strength is irrelevant because its function is not to restrain the movement (it cannot, in any case), but to deform and accommodate the movement without suffering functional damage. Comparing two materials installed on the same structure: (i) The membrane with a lower tensile strength and lower E modulus may well fulfill this function and retain its waterproofing integrity so long as the movement is within its deformation limit, (ii) The other material, on the other hand, with a higher tensile strength and higher modulus (stiffer) may fracture because the elevated stress needed to deform it exceeds its tensile strength. Or, if the built-up tensile stresses overcome its adhesion strength, it will delaminate, allowing the lateral migration of water between the membrane and the substrate in case of leaks thus compromising its waterproofing performance. In general, tensile strength is important during handling and installation of pre-formed membranes and for loose-laid or mechanically-fixed membranes. b) How important is the elongation value? The ability of waterproofing membranes to stretch and elongate under stress is undoubtedly important in applications where the substrate is subjected to movement such as on roof slabs. However, the elongation value, taken in isolation, is often misleading. Superficially, a material with 800 % ultimate elongation looks far superior to another with 300 % elongation. But conside r these points: Very high elongation values are usually achieved by materials with plastic deformation behaviour or elastic materials which have been stretched beyond their elastic limits. This raises two concerns- (i) Over the expected s ervice life of the waterproofing membrane, stress cycles in the
support structure are repeated countless times. Therefore, plastic elongation with
little or no recovery does not measure the membrane’s performance durability; (ii) Elongation is achieved at the expense of the membrane thinning out. For materials
subjected to very high elongation, this thinning effect would have stretched it way
past its useful thickness well before breakage occurs. In view of the above, waterproofing membranes are often reinforced with fabrics; these are built-in for preformed sheets and added during installation for liquid-applied membranes. They serve to add elasticity (recovery property) and/or restrict the elongation within useful limits. Therefore, for a waterproofing membrane applied on structures subject to movement stresses, the elongation value on its own is not sufficient for assessing its fitness for purpose. The important performance property to look for is its dynamic crack-bridging or crack-cycling capability, tested to recognised standards eg EN 1062-7. This test measures the membrane’s ability to elongate and recover over repeated cycles, simulating conditions you would expect the membrane to undergo during its service life. (Reference must be made to the manufacturer’s technical data sheet for instructions on use of particular products.) - Thank You -
Built For The Oceans
Writer: Leonard Wee Date: 27.01.2021 The oceans cover 71% of the world’s surface and contain 97.2% of the Earth’s water. With the increase of human population, effects of pollution on the oceans have also drastically increased, putting ecosystems and fish stock in jeopardy. According to the United Nations, many marine species worldwide are affected by marine debris, and as much as 80% of that litter is plastic. One of the best platforms to educate future generations about the effects of pollution on our planet are public oceanariums. They offer a “true world experience” in a controlled environment, which can be used for creating awareness, learning and inspiring change of habits for a cleaner environment. Bringing the ocean into a building is not a simple task. A huge amount of technology and husbandry know-how is required to bring an ocean ecosystem into an oceanarium tank. Construction methods to build these specialized concrete tanks require specific needs in order not to destabilize the exhibit’s water parameters while combating any possible structural deterioration from seawater. Fig. 1a: Oceanarium 3 million litres per hour non-metallic recirculation system Fig 1b: Oceanarium automated filtration system Seawater contains about 3.5% soluble salts (chlorides and sulfates) by weight and has a pH of around 7.5 to 8.4. It is a catalyst for corrosion, and like any exposed concrete structure to seawater in nature, direct exposure may deteriorate concrete through the effects of various chemical and physical processes. For example; • Sulfate attack • Leaching of Lime (Calcium hydroxide) • Alkali-aggregate expansion • Salt crystallization from wetting and drying • Corrosion of embedded reinforcing Controlling or stopping the deterioration through these processes is best done by reducing concrete permeability. Low permeability not only prevents tank leakage but, it also helps to keep seawater out of the concrete, thus slowing leaching and protecting the reinforcement steel from corrosion. Newly laid bare concrete, in whatever form, leaches when submersed in seawater. Leaching is very dangerous and lethal for an aquarium inhabitant causing spikes in pH and leaching of chemicals into the exhibit’s water column. The trick to building a successful oceanarium tank is a good waterproofing tank system and most importantly, to get it right the first time, as not to jeopardize the fishes when introduced into the tank. An oceanarium concrete tank structure can be grouped into 3 exposure zones; submerged, splash and atmospheric. The submerged zone is continuously covered by seawater, the splash zone is subject to wetting and drying and the atmospheric zone is exposed to seawater spray. Concrete in the submerged zone is not as vulnerable to corrosion compared to the 2 other zones. Oxidation works slower when submersed, but the flip side is that the leaching of lime can be fatal to fishes. Moreover, if metallic corrosion does happen underwater, the effects can be detrimental to some species, affecting the nervous and navigation system of most elasmobranchs (sharks and rays). Damage of concrete due to deterioration is like cancer; it slowly eats into your reinforced structure and spreads from there, increasing porosity and permeability to the concrete. There are multiple ways and systems available in the market that reduces permeability in the concrete but nothing beats a good lining system. Choosing a high strength, low permeability concrete mix with a minimum reinforcement cover of 50mm and a good non-toxic lining systems (eg. pure polyurea etc.) goes a long way towards creating a maintenance free and long service life concrete in a marine environment while keeping the fishes safe from contamination. Although a good design mix is a good start in ensuring a long concrete life, one must not forget that design and construction practices will affect strength, permeability and durability. We have found that a good lining system and low permeable base concrete base makes the worries go away. The reliability that every inch of concrete is placed properly in good construction practices can be a worrisome task and not practical for large tanks and areas. In addition, probable issues of external groundwater damages in structures below the water table are inherently difficult to identify. Lining systems like pure polyurea have revolutionized the construction and waterproofing of oceanarium tanks because it reduces the risk of permeability problems and the quick cure time allows work for other trades to continue efficiently. Fig 2a: Poorly placed new reinforced concrete tank that required rectification. Fig 2b: New reinforced concrete with lesser than 50mm cover Like with any protection membrane installation, a good base concrete is extremely important, as it (the lining) would be considered as the first line of defense and concrete cover as the second, before seawater reaches the reinforcing. In addition to this, high-risk areas for corrosion in seawater such as construction joints can be mitigated. It is found that with systems like these, localized rebar corrosion from construction joints and cracks is reduced drastically. Fig. 3a: Typical concrete tank surface preparation Fig. 3b: Pure polyurea waterproof lining system application In order to have a composite system to fully work together, the chemical bonding of lining and concrete plays a very important role. Proper moisture mapping, surface preparation and application are key in the laying of a 3mm pure polyurea lining system. Other key procedures such as viewing panel silicone bonding test between polyurea lining and the acrylic prior to installation, helps ensure all these material components are fully integrated and watertight. Fig 4: Silicone chemical bonding test to acrylic viewing system and waterproofing lining system, where the best primer is selected Fig. 5: Completed tank with aquascaping and fish (inhabitant) introduction In conclusion, bringing the ocean and encapsulating it into a tank is truly a unique multi faceted task and its poses a unique set of problems to overcome. When building an oceanarium, it is important that designers are fully educated in the nature of seawater and the importance of the details in specifying marine structure corrosion mitigation systems. Having the right specialist from the start is also the utmost importance, where proper structural mix and lining system are selected with experienced on-site quality control managed, so that inhabitants of the oceanarium is safe and the nature of the oceans can be truly appreciated. - Thank you -
Crack Injection: For Show or For Real?
Date: 28/12/2020 Written by: James Lim #crackinjection #pugrouting #puinjection #injectionpacker #injectionpump #seepage #wetcrack #epoxyinjection #resingrout When we observe a crack on concrete slab or beam, we can either patch it with something to close it or we can seal it with a high strength resin which provides compressive strength and bond strength. For this, engineers prefer epoxy resin because it has strength and good bonding properties. Most epoxy resin available in the market caters for dry cracks condition as epoxy resin will not set when it is mixed with water. For wet cracks, either underwater epoxy resin or high strength polyurethane resin shall be selected for crack injection. In this respect, 2 components polyurethane resin is ideal as it will react with the water to form a stiff material with a bonding strength of 1.5 N/mm2. It is important to know that structural polyurethane resin can achieve a compressive strength of 80 MPa and this is equivalent to the strength of an epoxy resin. Upon contact with water, polyurethane resin forms a rigid structure that does not allow air and water to pass through the cracks. When the cracks are sealed and air tight, corrosion of the steel reinforcement can be prevented. At the job site, it is not difficult to spot a group of injection nipples or injection packers sticking out along the line of crack to illustrate the repair job is completed by visual inspection. Now the question to ask is whether the resin has penetrated into the cracks as intended by the structural engineers who specified the method of repair. Surprising enough, nobody seems to be interested in asking whether the cracks are sealed properly. The sight of seeing rows of injection nipples or packers basically confirmed that the job was done as intended. So it is basically good showmanship because we don’t normally questioned whether the cracks have been properly sealed with injection resin or not. If you were to conduct a random test to check the resin penetration by core sampling test, you will notice most of the cracks are not filled with resin due to poor injection methodology. As engineers are not trained to recognized whether the specialist applicator has done a good job, the outcomes are often left for imagination. This is because the showmanship of crafting the rows of injection packers were suffice to confirm the job was done to reasonable standard. No further tests or quality control are put in place to ensure the resin actually penetrate the cracks. So real injection or great showmanship? The easiest way of finding out whether the injection is good is by looking at the way how the holes were drilled. The drilled hole is the only passage for the resin to travel into the crack. As simple as it may seems, drilled holes that are not drilled deep enough to intercept the cracks are likely to result in a road block situation. Road block means injecting resin into a solid wall of concrete because the holes were too shallow. To intercept the crack effectively, a drilling angle of 45 degrees are recommended versus drilling perpendicular to the concrete surface because the cracks are often not straight when you take a cross section view of the cracks. For method that uses surface packer or injection nipple where only epoxy adhesive is used to bond the nipple to the concrete, the injection resin could not travel far into the cracks because surface packer or nipple are not designed to handle high injection pressure. Low injection pressure limits the penetration depth of the resin and it is likely to result in incomplete filling of the cracks or even no fill at all if the packers/nipples were not aligned with the crack. Repair specialist prefers this method because it is quick and easy to do since drilling is not required. But it is often more of a showmanship to show the structural engineer that injection has been done to seal the cracks. What can we observe from the site picture taken above? 1. Do you need that many holes for an injection job? What surprises the most is that the contractor was even allowed to drill so many holes in a small area. 2. Inconsistent drilling angle. The bottom row is drilled at an angle and the upper rows were kind of perpendicular to the wall. Potential honeycomb location to inject perhaps. 3. Resin rebound back at the location of the packer and this indicates a road block situation. Therefore, injecting into solid concrete. 4. Injection packers were left on site. Perhaps to show proof of injection by showing the number of packers installed. With a perfect hole that connects the cracks to a high pressure piston injection pump, the chances are you will not require to drill as many holes as seen in picture above. The one with the most number of packers are the likely outcome of an amateur contractor with good showmanship. Unless the structural engineer requires to fill and bond the cracks properly, the injection shall be done with diagonal drilled holes staggered at both sides of the crack and then inject it with a high strength resin. With good drilled holes achieved, the required injection pressure should not be more than 1000 psi at the start and it will quickly drop to 300 psi when the resin starts to flow into the cracks. The concept of injection consists of an understanding of 3 elements below: 1. Connecting the cracks/zone of injection with a drill hole. Mostly like a longer drill bit to hit the spot. 2. Injection pressure. The key is to achieve consistent injection pressure during the process of injection. 3. Injection resin mix ratio and setting time. An ultra-fast setting resin requires a plural pump set up and built-in flushing capability. As simple as it might seems, real injection requires careful planning of packer position, resin selection and choice of injection pump. Asking the right questions in the process of resin selection and injection methodology will allow the engineers to get a better outcome when it comes to crack injection. -Thank you-
Roof Waterproofing Trends and Polyurea Solutions
Date: 01/12/2020 By: Mr. Tan Ju Kuang Constructing a roof, be it a concrete or metal roof can be an easy task for a typical roofing contractor. Concrete roof slabs are usually built with a waterproofing system that is designed with conventional system such as crystallization admixture, exposed EPDM membrane, liquid applied membrane such as acrylics and polyurethane coatings. Other than concrete roof, metal decking roof is also popular in factory construction where the metal sheet naturally provides the waterproofing properties it needed for a factory set up. Metal sheets overlap each other and fasteners provided the anchoring requirement to hold the metal deck in place. Concrete are prone to cracks due to shrinkage and cracks could compromise the waterproofing membrane at the flat roof. Similarly, metal deck and metal screws corrode over time and this could lead to issue relating to water seepage. This can be a pressing issue when the roof starts to leak and a solution is required. Started in the early 80’s, standard roof coating systems use to treat concrete roofs from further leaks include cementitious coating, torched on Bituminous Membrane, rolled on acrylics coatings and polyurethane coatings. Conventional coatings like these while they offer certain benefits, would not be considered a long-term solution today. Most of them could not be exposed to UV directly as UV’s will degrade the system causing premature failure of the coating or membrane. Epoxies and cementitious coatings are very rigid and are not designed to handle cracks due to poor elongation properties. Epoxies are likely to chalk and polyurethanes will degrade when exposed to the tropical climate with high UV and thermal expansion. In addition, the majority of the waterproofing membranes require a layer of protection screed to be laid over it. When this conventional system fails and the roof starts to leak, an exposed waterproofing with high abrasion resistance and stable under the UV is ideal for a re-waterproofing purpose as you do not have to remove the existing screed and waterproofed membrane and just lay the new membrane over it. Introducing Polyurea. Polyurea is a spray on elastomeric system which can be applied on both concrete and metal roof to resolve problem associated with water seepage. Polyurea can be applied to a thickness of 2-3mm, which will then give you an elongation property above 300% and a tensile strength of >15Mpa. Sprayed as a single coat system, it eliminates joints and overlapping within the coating itself and hence reducing the chances of leak from happening. As a roof coating repair system, it can be sprayed directly on existing surface after sufficient surface preparation is done, thus reducing the need to hack and remove existing screed which could be costly and time consuming. Furthermore, the shut down time of the affected areas can be reduced to a minimal due to the quick set nature of the polyurea resin, typically in less than 2 minutes after sprayed. Nevertheless, polyurea does have its limitations. The application of polyurea requires the operator to be skilled and well trained as the operation requires multiple set up of spray machine, air dryer and air compressor. The cost of maintenance of the spray machine and accessories can be high as the machine are supplied by niche vendors in the market. Depsite all the advantages it brings, the polyurea system also comes at a higher cost compared to conventional waterproofing system. The cost factor of this system often discourages wide spread use of polyurea for customer who understand its cost benefit analysis. The growing trend of green roofs being designed and built in the country also mean that conventional waterproofing with joints/seams will not work as root penetration attack on the coating itself can be an issue. In this case, polyurea are ideal as many product manufacturers have test their polyurea for anti-root penetration. Among other typical uses of polyurea coating includes portable drinking water tank lining systems which required local authority drinking water certificates, theme park coating where coatings are subject to constant immersion of chlorine and UV exposure as well as foot traffic.
Is Water Ponding on Carpark Floors Normal?
Date: 15.07.2020 By: Dr. Zack Lim Nowadays water ponding has become a common construction dispute as any water appearing stagnant on the floor surface us generally not acceptable by owners and/ or architects. Hence, is water ponding normal or should it be rectified? Two issues are commonly encountered when rectification is made to water ponding. Firstly, if the affected area is rectified, there is a tendency that a new puddle of water my be created adjacent to the rectified area. Secondly, it is very difficult to carry out thin topping repairs on low areas successfully. Any mason can repair a floor but what is the assurance that the repaired area will not delaminate or fail months later? Before understanding the causes and finding a solution, everyone should know the difference between 'flat' and 'level'. Flatness relates to the bumpiness of the floor surface and levelness relates to the tilt or slope of the floor. To describe a floor profile clearly, flat and level are two inseparable entities with different types of floor profile as shown in Fig 1. Water ponding is common on concrete floor surfaces, especially at today's large carpark areas. This problem is unavoidable as most finished floor levels are specified to meet a 'perfect level', and even on a floor that is constructed to be super-flat and super-level, the water will still stagnate on the floor surface as the water has nowhere to fall. Therefore, the only way to eliminate ponding problem is to design and build the floor surface to fall or slope to facilitate water flow. Thus, the expectation of the property owners and architects by not having any water ponding (unless to fall) is not realistic. There must be an acceptance of reasonable tolerance on the level of ponding. What causes water ponding? Large areas of water ponding or small localised ponding known as birdbaths are results of depressions created on the concrete floor surface during concrete strike-off (screeding) and power trowelling. The other reason for water ponding can be resulted by a deflection of a floor slab caused by the weight of the slab itself after the removal of scaffoldings or a possible change of floor profile on an elevated slab after post-tensioning the slab. Idealistically, to avoid water ponding, concrete floor need to be built with a surface profile that is very flat but not level (designed to fall), to cater for water runoff from a higher to lower elevation. However, modern carpark floors are so large that it is impractical to build floors with gradients, as concrete at the centre need to be much thicker to enable water to fall to the lower perimeter scupper drains. Alternatively, the formworks to receive the concrete can be installed to tent-shape so that the concrete can be laid with consistent thickness with falls. However, it is extremely difficult for builders to actually control and do it precisely. As floors are generally designed and built without gradients, any high spots will restrict water to flow freely to any low-lying areas which then trap and hold water, resulting in water ponding. Floor specification and acceptance The QLASSIC standard mentioned that specification for floor surface evenness allowed is 3mm over 1.2-meter starightedge whereas BS8204-2:2003 (refer Table 1) has three classifications of floor flatness for different usages. For example, SR3 specification, which is a 10mm tolerance under 2-meter straightedge is generally recommended for carpark floors. Fig 2 shows how a SR floor is measured using a 2-meter straightedge placed anywhere on the entire floor surface and uses a slip-gauge to measure the gap under the straightedge. This only measures the flatness of the floor but does not measure the level tolerance from the control datum or finished floor level (FFL). As mentioned earlier, flat and level are two inseparable entities, therefore floor level tolerance also needs to be specified for the entire finished floor. For example, +/- 15mm tolerance from the finished floor level is a very stringent specification imposed on levelness control. If a level tolerance of +/- 15mm is also specified from the finished floor level, logically water ponding of up to 30mm may be observed over the entire floor area. Rectification of water ponding Generally, the method of repair is carried put by grinding the high spots that caused water damming and topping up the low areas with suitable cementitious materials. However, if the high areas are grinded down too much, it will cause new ponding areas around the newly filled up areas. As such, rectification works to eliminate water ponding may backfire as most repair areas will looked worse than original and any repairs not carried out professionally may results in delamination. It is near impossible to build a concrete floor with no water ponding. As such, if the depth of water ponding is very little (not more than 10mm deep), it is bearable and acceptable as it can easily be removed. As today's carparks are mostly dry, any slight imperfections on the floor profiles are unnoticeable when dry. Low spots are evident only if waters is present. Understanding of Surface Regularity (SR) Theoretically, a floor specified to SR2 tolerance accepts 5mm water ponding on every localised measurement using a 2-meter straightedge. However, the common misinterpretation of SR2 is assumed to be a +/- 5mm level tolerance from the control datum (level control), which is near to impossible to achieve. As a result, huge spending for repairs are incurred due to such misunderstandings in complying to the SR standard. Another ambiguity of this standard is that it does not indicate how many bumps are allowed if measurements need to be taken. Generally, at least 5% of the floor area should be measured. For example, for a floor area of 500-square meters, twenty-five equally spaced out points need to be selected and measured randomly. Conclusion Without water stagnation on the floor, any low spots may not be noticeable. Any corrective action taken on insignificant ponding areas is unfavourable, as any repair carried out may make the smooth floor appear worse than before. If the repairs is not carried out properly, in addition to patchiness and colour variations, the repaired area may delaminate. The only areas where water ponding is unacceptable are main walk paths, vehicle turning points and areas which may be a safety hazard, causing people to slip and fall or a vehicle to skid. Thank you
Stamped Concrete Finish in Malaysia – An Introduction
Date:05 April 2020 By :Eric L.S, Soong Simon K.K, Soong #stampedconcrete #concreteimprint #textureconcrete Stamped concrete popularized in the United States in the 1970s was beginning to make its way to Malaysia in the late 1980s. The systematic method of concrete stamping was introduced by a gentleman named Brad Bowman in the 1950s. After making its foray into Malaysia, this new trend of decorating concrete began slowly to gain momentum in the county. Once dominated by plain concrete finishes, interlocking pavers and floor tiles, today stamped concrete has been trending throughout the county and found favour among the local architects and designers. Stamped concrete exhibits a unique trait in being able to blend a variety of colors and patterns together. This special property is what makes it a popular feature for decorating roads, driveways, walkways, patios and many more places. It also offers a variety of pattern options ranging from wood textures to slate textures. Other benefits of using stamped concrete include among others its affordability, the durability of the product and its requirement of not needing much maintenance. The Early Years In the early years of stamped concrete, the works were largely concentrated in individual luxury houses. In the late 1980s and early 1990s as the trend began to pick up, stamped concrete was being installed in larger volume and scale. Stamped concrete began to feature prominently in many housing developments as it accords a uniqueness to the development. Specifically the stamped concrete works in these developments would generally adopt a single pattern with a two- tone color system to attain a more realistic feel to the design. The blending of colors were typically achieved by combining different products such as colored release powders The Later Years Forty years since stamped concrete was first introduced in Malaysia, it continues to be one of the pillars in both the residential and commercial building sector and is a common product offered among decorative concrete contractors. However, customization and differentiating designs are the new normal in this day and age. Designers and architects are now adding their creative touches to the finishing design by using existing moulds and other decorative products to give it a unique outlook. In order to realize this new feat, contractors are turning to hand tools to create the finer designs such as customized groove and post coloring techniques, for example stains, to blend multiple colors. Challenges The stamped concrete industry do have its challenges. Some of the challenges encountered by decorative concrete contractors often include, among others, issues such as surface delamination, crusting cracks and lack of pristine textures on the final product. Many contractors shared the common problem on surface delamination, though in many ways it is not a reflection of the stamped concrete product itself. The main culprit more often than not is that insufficient time to allow the excessive bleed water to escape before broadcasting the color hardener onto the concrete surface. A little concrete bleeding will be beneficial to facilitate working with the dry shake color hardener but excessive concrete bleeding is one of the causes for delamination when the bleed water and air accumulated under the dense hardened color hardener, unable to escape. Another major cause of delamination is over-layering resulted from broadcasting the color hardener onto hardened concrete, followed by wetting and floating the surface. This issue can be mitigated by adjusting the concrete mix design to reduce concrete bleed water and to improve the workability with sufficient time for finishing. Crusting cracks is another issue seen on some finished works. Whilst the cracks themselves do not generally affect the durability of the concrete slab; their appearance is unsightly on the finished product. These cracks are mainly found near the stamped joints near the edges of the imprinted texture. This occurs as the surface loses water rapidly and has hardened before the rest of the concrete is allowed to set and tends to amplify during hot and windy days. Small cracks are formed around the stamped joints as the stamp mats are pushed into the crusted surface, and the surface tears apart due to stresses. This issue however could minimized by erecting a shade when casting during a hot day and by putting up temporary wind barriers to reduce the wind velocity on the surfaces. Lack of texture on the finished products is a common issue faced in the industry. A major factor that causes this issue is the type of concrete mix used during the stamping process. Concrete mix with large amount of coarse aggregates could interfere with the impression of the stamping process. One way that this could be minimised is to thus ensure the appropriate size and type of aggregates contained in the concrete mix, and in this regard, the experience of the decorative concrete contractor matters. Moving Forward A better understanding of concrete behavior and how the work surroundings could impact upon the final product are essential in bringing up, and capitalizing on, the many great features accorded by decorative stamped concrete products. These factors together with the growing diversity in stamped concrete designs as well as the continuing advancement in concrete technology in Malaysia will be strong sustaining driving forces to propel the decorative stamped concrete industry forward.
Pigmented Concrete Facade Finishing (Part 1)
Date: 9 April 2020 By: Oscar R.H.Teng Tony Teng #GFRC #GRC #Façade #Pigmented #Concrete Façade, have you ever wondered how do you read this word? Have you come across this word around while being in the construction industry? There have been multiple pronunciations in the construction industry especially in Malaysia. According to the Cambridge Dictionary, the proper pronunciation is /fəˈsɑːd/ (Cambridge University Press, 2020), which in other words, it is similar to “Far – Sud”. According to the above dictionary, façade is defined as; the front of a building, especially a large or attractive building (Cambridge University Press, 2020) where in lay-man term, the make-up of the building. Among the range of façade materials, concrete façade has its own unique character. It is believed that concrete façade serves to bridge between the design of ancient stone façade of castle like buildings to modernized unique curvy designs. This is due to concrete being ‘malleable’ which enable the shape of the concrete to be limitless as long as the mould can be fabricated. With the advancement of concrete technology and knowledge, concrete façade has developed from painted concrete to stained concrete and further to pigmented concrete as the replacement of conventionally dull color concrete. To further explain pigmented concrete, it is the mixture of color pigments dispersing in the medium of cement mortar (binder) in order to create colored concrete when cured. One of the recent building in Malaysia was constructed with it’s entire building covered with pigmented concrete as their façade curtain wall with combinations of aluminium-frame and glass is The Chow Kit Hotel located in Kuala Lumpur, Malaysia. Unsurprisingly, such distinguish design has won itself multiple press featurings including but not limited to; Monocle (UK);’Key Opening’ and The New York Time Onlne; ’52 Place To Go in 2020’ (Ormond Group, 2019). The beauty of pigmented façade is the huge contrast of color depending on the time, light, and weather effect on the concrete. With all theses features, this is one of the reason why The Chow Kit was featured. At noon, the façade is more towards brown in color while evening, the color will turn slightly reddish. Even better, as night falls, the building will appear more amazing when the color appear to be brownish-red especially when the spot lights illuminated the façade. (Left)The Chow Kit by Ormond Group, evening sun (Ormond Group, 2019) (Right)Side view of The Chow Kit by Ormond Group, night view(Ormond Group, 2019) Apart from Malaysia, pigmented concrete is being used all over the world as façade. Pigmented concrete can be shaped into different shapes just like normal concrete. Below are some buildings from all over the world which are featured in both ‘Archdaily‘ website that present architecturally interesting building internationally and ‘Concrete Construction’ website where usage of concrete is often discussed. The Casa das Historias Paula Rego (ArchDaily, 2020) Built in year 2008, designed by architect Eduardo Souto de Moura. This building have two iconic red pigmented concrete pyramid-shape towers. Being a museum, having a timeless design using pigmented concrete has always been a choice by many architects. L23 House (ArchDaily, 2020) Built in 2011, designed by Pitagoras Group. This is a private house located on a slope of a higher point of Guimaraes city, Portugal. In order to outstand the house itself on a slope full of greens, black pigmented concrete façade was selected as a contrast on the hill. Textilmacher (ArchDaily, 2020) Built in 2013, designed by Tillicharchitektur. Textilmacher is an office building/showroom located in Munich, Germany. The building is designed for a company that does textile print and embroidery. Hence, the iconic geometry folded design is combined with grey pigmented concrete façade to represent the character of the textile company. Nevertheless, depending on the season, time, light shining on the building and the weather, the pigmented façade will change it character continuously. Pigmented concrete façade is not limited to rectangular panels but can be designed to any forms. With different texture/shapes of pigmented concrete, we can achieve various kinds of finishing effects. We shall discuss about the finishing textures available for pigmented concrete in the next article. TO BE CONTINUED References ArchDaily. (2020, Mar 24). The Possibilities of Pigmented Concrete: 18 Buildings Infused With Color. Retrieved from ArchDaily: https://www.archdaily.com/910825/the-possibilities-of-pigmented-concrete-18-buildings-infused-with-color Cambridge University Press. (2020). Cambridge Dictionary. Retrieved from https://dictionary.cambridge.org/dictionary/english/facade LUXBEE. (2019). Chow Kit Hotel work in progress. Retrieved from Facebook: https://scontent.fkul14-1.fna.fbcdn.net/v/t1.0-9/p720x720/71406407_1506170862871243_3333448393304309760_o.jpg?_nc_cat=107&_nc_sid=8024bb&_nc_ohc=L2ljKWTQjjYAX-1DmhA&_nc_ht=scontent.fkul14-1.fna&_nc_tp=6&oh=5c15de8635c0145aa38bfe637ae51359&oe=5E9D0B0F Ormond Group. (2019). The Chow Kit. Retrieved from Press: https://www.thechowkit.com/press Ormond Group. (2019). The Chow Kit. Retrieved from Gallery: https://www.thechowkit.com/gallery