Building Cladding

Cladding is the application of one material over another to provide a skin or layer intended to control the infiltration of weather elements such as wind, rain extreme heat etc or for aesthetic purposes. Often time building cladding does not necessarily have to provide a waterproof condition but in some situations can be applied as a control element. Cladding as a control element may only serve to safely direct water or wind in order to control run-off of the same and prevent infiltration into the building structure.

As with all other exposed portions of the building enclosure (windows, roofs and balconies), regular review and maintenance of the cladding is important to ensure intended performance and appearance. Cladding is the first line of defense in a wall assembly. It is critical for protection of the more sensitive components of the wall assembly and the interior of the building. Proper maintenance of the cladding will reduce the likelihood of water penetration and preserve the appearance of the building. Wear and tear on cladding is expected since it is continually exposed to sun, rain, wind and temperature changes. In addition, cladding is subject to damage due to accidents, vandalism and excessive vegetation growth.

Cladding has become one of the most popular alternatives for renovating the exterior of existing buildings as it gives a building a new look and a new life.  Cladding benefits are greatest when dealing with high story buildings or buildings confined in a small site, where demolishing process is almost impossible and not feasible.

Benefits of Building Cladding

Aesthetics is a huge factor when dealing with wall cladding projects. Several solutions have become available that minimize system depth at the same time achieving the expected aesthetic. Some of the benefits that arise with the cladding process are:

• Prolonged service life of the structure

• Rise in revenue and value of the building (commercial buildings)

• Improved appearance and beauty of structure

• Improvement of thermal acoustic and natural daylight performance

• Protection of the structure from water penetration and improvement air tightness

• Lowers maintenance costs and allows upgrading of building services

 

Enhancing the Beauty of your Home through Landscaping 2

 Waterfalls

In most cases you will find people investing in devices that produce a sound of waterfall. They place them in the living room or on their work desks and recreate the scene of a small waterfall to help them relax. Why not construct a larger one on your property? Your waterfall could be a constant focal point for relaxation as you develop exactly what you want to see and hear using natural materials. You can lavishly decorate your waterfall with plants, creating a unique look that can remove pollutants from the air and water as it soothes. Many waterfalls can run on solar-powered pumps so you don’t have to worry about huge electricity bills.

 Ponds

You can construct small ponds in the compound to house marine life to further accentuate the scene. A pond built with natural materials can give it a unique presence that will catch the eye of passers-by. Some ponds are large enough that designers will even construct small footbridges over them to enhance the experience. Apart from just serving as a beauty enhancement spot on your property, you can stock the ponds with fish and this can serve a source food.

 Native Flowerbeds

 Developing a nicely decorated flowerbed is one of the cheapest ways to enhance the look of your compound. When doing native flowerbeds go for native species that allows you to do more than beautify. Growing the plants native to your area can better as they require less maintenance, perform well from season to season, and support the insect life that supports native birds. As well, the native plants that you grow will give your garden a sense of belonging.

Natural landscaping doesn't have to cost you a lot of money. You can do the work by yourself. However, it will require patience and time as you grow seeds into flowers and sculpt rocks. Doing your own landscaping has hidden benefits, like reducing stress and providing exercise.

Segregation in Concrete

Segregation is a process by which large aggregates separate small aggregates and is normally caused by pouring concrete from heights of more than one meter.

To obtain a good concrete all the ingredients must be properly distributed so that a homogeneous mixture is achieved. There is considerable difference in the sizes and specific gravities of the constituent ingredients of concrete making it natural that the materials show a tendency to fall apart.

A concrete that is well mixed by taking into consideration various parameters such as grading, size, shape and surface texture of aggregate with optimum quantity of water will result into a good cohesive mix thus limiting the chances for segregation. The cohesive and fatty characteristic of the concrete mix does not allow the aggregate to fall apart and at the same time it plays a crucial role in containing the aggregate by denying water an easy way to drain out freely from the rest of the ingredients.

The conditions that make concrete prone to segregation include;

• Badly proportioned mix with absence of sufficient matrix to bind and contain the aggregates. 

• Insufficiently mixed concrete with excess water content. 

• Dropping of concrete from high heights as in the case of placing concrete in column concreting. 

• When concrete is discharged from a badly designed mixer, or from a mixer with worn out blades. 

• Conveyance of concrete by conveyor belts, wheel barrow, long distance haul by dumper, long lift by skip and hoist are the other situations promoting segregation of concrete. 

• Lack of sufficient vibration. Vibration of concrete is one of the important methods of compaction. It should be remembered that only comparatively dry mix should be vibrated. It should be noted that vibration is continued just for required time for optimum results. If it is overdone particularly in a too wet mix, it is likely to result in segregation of concrete due to settlement of coarse aggregate in matrix.

Segregation can be avoided by; 

•     Properly following the right concrete mix-design. 

•     Mixing concrete ingredients properly. 

•     Maintaining the correct water-cement ratio. 

•     Not dropping concrete from too high heights during placing. 

•     Avoiding over vibration of the concrete.

Bleeding in Concrete

Bleeding in Concrete

Bleeding is a form of segregation where some of the water in the concrete tends to rise to the surface of the freshly placed material. This arises due to the inability of the solid components of the concrete to hold all of the mixing water when they settle downwards (water being the lightest of all the mix constituents). Bleeding of the water continues until the cement paste has stiffened enough to end the sedimentation process.

Remixing of the bleed water during the finishing of the top surface must be avoided as this will result into a weak top surface. To avoid this, the finishing operations can be delayed until the bleed water has evaporated. Conversely, if evaporation of the surface water is faster than the rate of bleed then plastic shrinkage cracking may occur.

Bleeding is predominantly observed in a highly wet mix, badly proportioned and insufficiently mixed concrete. In thin members like roof slab and when concrete is placed in sunny weather excessive bleeding is bound to occur.

Due to bleeding, water comes up and accumulates at the surface. Sometimes, along with this water, certain quantity of cement also comes to the surface. When the surface is worked up with the trowel, the aggregate goes down and the cement and water come up to the top surface. This formation of cement paste at the surface is known as “Laitance” and this causes the top surface of slabs not to have good wearing quality.

Water while traversing from bottom to top, makes continuous channels. If the water cement ratio used is more than 0.7, the bleeding channels will remain continuous and un- segmented. These continuous bleeding channels are often responsible for causing permeability of the concrete structures. While the mixing water is in the process of coming up, it may be intercepted by aggregates. The bleeding water is likely to accumulate below the aggregate. This accumulation of water creates water voids and reduces the bond between the aggregates and the paste.

The above aspect is more pronounced in the case of flaky aggregate. Similarly, the water that accumulates below the reinforcing bars reduces the bond between the reinforcement and the concrete. The poor bond between the aggregate and the paste or the reinforcement and the paste due to bleeding can be remedied by re vibration of concrete. The formation of laitance and the consequent bad effect can be reduced by delayed finishing operations.

Bleeding rate increases with time up to about one hour or so and thereafter the rate decreases but continues more or less till the final setting time of cement.
  

 Prevention of Bleeding in concrete

• Bleeding can be reduced by proper proportioning and uniform and complete mixing. 

• Use of finely divided pozzolanic materials reduces bleeding by creating a longer path for the water to traverse. 

• Bleeding can be reduced by the use of finer cement or cement with low alkali content. Rich mixes are less susceptible to bleeding than lean mixes.

The bleeding is not completely harmful if the rate of evaporation of water from the surface is equal to the rate of bleeding. Removal of water ( after it has played its role in providing workability) from the body of concrete by way of bleeding will do good to the concrete.

Early bleeding when the concrete mass is fully plastic may not cause much harm because concrete being in a fully plastic condition at that stage will get subsided and compacted. It is in the delayed bleeding state and when the concrete has lost its plasticity that undue harm is caused to the concrete. Controlled re vibration may be adopted to overcome the bad effect of bleeding.

Concrete and its Properties 2

Concrete is the pourable mixture of cement, water, sand, and gravel that hardens into a super-strong building material. Concrete is commonly used to cast building foundations, sidewalks, slabs and columns and even highways are all made of concrete.

Proportioning and mixing concrete

The proportion of each material in the concrete mixture affects the strength and durability of the final hardened concrete. Though measurement by volume is suitable for minor projects in large scale projects the proportions are best determined by means of weight as the use of volume may not be as accurate. When proportioning the concrete mixture the environment in which the concrete is to be used should be carefully considered; ie exposure to sea water, trucks, cars, forklifts, foot traffic or extremes of hot and cold.

A good concrete mix should produce concrete that is easily workable, cohesive when plastic and can be easily placed at a favorable cost. The mix should give a strong and durable concrete when it sets and hardens.

Properties of Concrete

Properties of concrete are divided into two major groups;

1. Fresh Concrete Properties

2. Hardened Concrete Properties

In this article and the subsequent series that will follow we shall focus our attention on Fresh Concrete, its properties, challenges and how to avoid them.

Fresh Concrete

Fresh concrete is the type of concrete that is still in its plastic form. This is also referred to as "Green Concrete".

Properties of Fresh Concrete

Properties that determine fresh concrete are;

•    Setting

•    Workability

•    Bleeding

•    Segregation

•    Hydration

•    Air Entrainment

1. Setting

Setting of concrete is the hardening of concrete before its hydration or before it gains strength.

Concrete setting is related to the setting of cement paste. Thus cement properties may greatly affect the setting time.
Some of the factors that influence or affect the setting of concrete include;

• Water-Cement ratio - It is water cement ratio that basically governs the setting of the concrete. The correct proportion of water cement ratio will guarantee a perfect and fast concrete setting.

• Type of cement - Cement affects the hydration process and therefore setting of concrete. Cement is the    paste that holds or binds all the ingredients. The quality of cementing material used greatly determines how well fast the setting will come out.

• Cement content - Cement content in the concrete mix should be in the right and advised quantity.

• Type of Aggregate - Rough and angular aggregates are preferable as they provide greater bonding.

Other factors include humidity and temperature.

Concrete and its Properties 1

This week we continue with the second part of our four part series on Concrete and its properties by considering the concrete work-ability.

Work-ability of Concrete

What is concrete work-ability? You may ask.

This is the ease with which concrete can be transported, placed and consolidated without excessive bleeding or segregation. For the concrete to be workable it should be consistent.  Consistence is sometimes taken to mean the degree of wetness. Within limits, wet concretes are more workable than dry concrete, but concrete of same consistence may vary in work-ability.

Because the strength of concrete is adversely and significantly affected by the presence of voids in the compacted mass, it is vital to achieve a maximum possible density. This requires sufficient work-ability for virtually full compaction to be possible using a reasonable amount of work under the given conditions. Presence of voids in concrete reduces the density and greatly reduces the strength of the concrete.

 Factors affecting concrete work-ability include;

1. Water content or Water Cement Ratio

More the water cement ratio more will be work-ability of concrete. Since by simply adding water the inter particle lubrication is increased. High water content results in a higher fluidity and greater workability. Increased water content also results in bleeding. another effect of increased water content can also be that cement slurry will escape through joints of form work.

High water content results in a higher fluidity and greater work-ability. Increased water content also results in bleeding.  Another effect of increased water content can also be that cement slurry will escape through joints of form work.

 2. Amount and type of Aggregate

  The greater the size of the aggregate the less water will be to lubricate it thus making available extra water for work-ability. Using smooth and round aggregate helps in increases the work-ability. Work-ability of the concrete may reduce in a case where angular and rough aggregate is used. Angular aggregates increase flakiness or elongation thus reducing work-ability. On the other hand round smooth aggregates require less water and less lubrication and it allows greater work-ability in a given water/cement ratio mix.

 3.  Aggregate Cement ratio

When the ratio of aggregate to cement is higher than recommended  the less the work-ability on the concrete will be since less cement means less water and this will result into a paste that is stiff thus reducing work-ability.

 4.  Weather Conditions

Weather conditions such as high temperature and strong winds affect both the setting and the work-ability of the concrete. Strong winds and high temperatures cause increase in the rate of evaporation leading to reduction in the amount of water in the concrete mix thus affecting work-ability.

 5. Chemical Admixtures

The use of certain chemical admixtures has been known to increase work-ability of the concrete. For instance the use of air en-training agent is known to produce air bubbles which act as a sort of ball bearing between particles and increases mobility and work-ability. This also helps to decrease bleeding and segregation. Use of fine Pozzolanic material produces better lubricating effect that helps in providing more work-ability.

 6.  Sand to Aggregate ratio

The higher the amount of sand in the concrete mix the more the work-ability will reduce. This is because sand has more surface area and more contact area and this may end up causing more resistance.

When preparing a concrete mix proportion the ingredients using the appropriate weight or volume. This will help to provide the desired strength and work-ability at minimum expense.

A low water-cement ratio may be applied to achieve a stronger concrete. It would therefore appear that by making the cement content high one could use enough for good work-ability and still have a low water/cement ratio. As true as it may be the problem is that cement is the most costly of the basic mix ingredients. 

Dealing with situations in construction

Dealing with situations in construction

Even in full working order, construction can be messy. No amount of process "innovation" seems to alter this basic reality. Owners today remain apprehensive about the risks of construction and the ability of designers and builders to reliably deliver. In what seems to be a nearly permanent state of demand for the next best thing, the marketplace is responding to calls for change of status quo project delivery paradigms. Project constituents never quite seem to catch up. Productivity suffers as the learning curve seems never-ending. However, when notice to proceed is given and schedule pressure takes hold, discussion of collaboration must give way to actual collaboration. One of the most valued collaborative skills for design professionals is expert proficiency in situational judgment. Situational judgment tells us how to go about solving the problem by first understanding what really constitutes the problem.

 What exactly constitutes a situation in construction? A situation usually means that a technical or process problem needs to be solved. It is a precarious moment that requires using proportional measures of delicate diplomacy and blunt talk.

 Construction situations demand that design professionals be part sleuth, part sage, part cool customer, and part improvisation list. This calls for a well-developed ability in areas of diagnostics, experience, mindset, and creativity. If diagnostic skill is all about analysis and discernment of what is relevant, then the foundation of that skill rests on our experience. Our experience is the repository of the knowledge that we use as a basis of comparison to identify with the elements of the situation. However, great diagnostic ability that is firmly rooted in solid experience is not enough. In the construction environment, problem solving is always under some form of duress. The "hurry up" mantra of schedule pressure, cost constraints, and expectations of quality all exert enormous influence on everything we do.  Under stressful conditions, our mindset is vital; it must promote action over paralysis.

 Lastly, we need to develop creative skills that synthesize solutions by using tools on hand, left to us by the situation. Emphasizing development in these four areas should be the goal of every professional involved in the construction process.