Technical Information Research & Building Construction Analysis

Technical Information Research & Building Construction Analysis

Task 1

i. Construction Stages

Site preparation

In all construction and building projects, site clearing is the initial phase and it involves the removal of trees, vegetation, and old or unwanted structures that sit on the prospective site, as was the case in the observed project. In accordance with the statements of Wilkie (2011), all services including water, gas, and power were disconnected from the structure before the demolition work began. Other services like drainage and stormwater were also sealed off, and the necessary steps are taken to ensure that the nearby properties are protected. One of these strategies was to fence the site and ensure appropriate barricading to prevent unauthorized access to the construction site (Wilkie 2011). After demolition, the rubble was cleared and excavation work began.

Figure 1. Site preparation - demolition of the previous structure

Various equipment can be used in the excavation phase. The choice of equipment to be used depends on the nature of the specific site. For this specific site, site preparation and excavation was done using an excavator, semi-trucks, Bobcat, Vertical rammers, tippers, and plate compactors (Department of training and workforce development 2012). The operation of all the equipment was done by trained professionals to ensure safety for everyone involved and that work was done to the required standards.

Figure 2. Site preparation – excavator

To ensure the site is completely level and that erosions and runoff are controlled, bobcats were used to level and grade the construction site. Grading is vital on a construction site for it helps to avert water flowing through the site and even for the foundation of a newly built structure. Grading in the current site was done by creating a slope away from the foundation of the structure (Department of Justice 2017). In addition, the ground was also leveled to ensure a perfectly level base for the foundation. Leveling was done using a builder’s auto-leveler, commonly known as the dumpy level.

Figure 3. Site leveled and fenced

Footings

The role of the footing is to carry the structure, form a base for the foundation, and to transmit the superimposed load of the structure to the ground. According to Wilkie (2011) and Department of Justice (2017), the type and the size of the materials should be proportionate enough to bear the load and suited to the condition of the soil. In the current construction project, excavation of the footings was done using an excavator. Piers were also used as the holes were dug using an excavator with an auger bit attached. Reinforced concrete was used for the footings.

Figure 4. Site preparation - excavator excavating for footing and foundation

After the footing, the slab was laid. A plastic sheet was used to function as the vapor barrier. The role of a vapor barrier is to prevent water from rising from the ground into the slab (Department of Justice 2017). The was in line with the AS 2870:2011 Residential slabs and footing standard clause 5.3.3.2(c) which requires that vapor barrier should be medium impact resistant. For the current construction project, a strip footing was sued that follows the structure’s walls, both external and internal. The footing thus uniformly distributes the load all through the structure. Both the strip footing and the slab have been reinforced with steel metal beams.

Figure 5. Site preparation - slab laid and wire mesh

In addition to the reinforced concrete used for the footing and the slab, waffle slabs were also used. The waffle slabs used where shipped to the site in prefabricated models. These were placed in waffle pods and connected using ribbed columns along the slab. Waffle pods consisted of equally spaced ribs with corresponding columns. A two-way ribbed system of waffle slab pods was reinforced with concrete cross-sections compromising of ribbed reinforcement, slab top wire mesh, voids depth and width, waffles slab thickness (Galeb and Atiyah 2011).

Figure 6. Site preparation - slab laying and precast Waffle slab

Floor

In the observed building project, piers were also used to support the concrete slab-and-beam floor. Pier holes were excavated along the location of the planned structure walls to carry the load of the structure and effectively carry it to the ground. The excavated piers had concrete poured to then a slab-and-beam floor system cast on the compressible void-former providing space for expansion of the soil (Standards Australia 2011). The piers were made of concrete and treated timber which was to an appropriate depth. The piers were then cut at the desired depth to allow for the casting of the floor.

Figure 7. Site preparation - pier holes

As required by the AS 3660.1, termite control systems were used in the current building project. In fact, various termite control systems have been used which include chemical control and physical barriers e.g. graded stone particles, and woven stainless steel wire mesh. The footing and the slab also have some termite prevention elements especially the use of a tight slab concrete.

A slab-on-ground type has been used for this structure. To make the slab firm and well anchored on the ground, adequately excavated beams are used. Waffle slabs that are placed near-ground level are also used with a grid of polystyrene foam as void formers that create a beams maze in between the pods (Standards Australia, 2011; Department of Justice 2017). Insulation, as is the requirement with conventional slabs, is placed beneath the floor panels, which is the current building is below the waffle slab pods.

An advantage of the current site is that is level, thus making it easy for lying of the various floor elements. After the ground was adequately compressed with a layer of gravel, plumbing was done, termite treatment done, then outside edge boards set. The entire area within the edge boards was covered with plastic sheeting, then a layer of wire mesh. Next was a layer of waffle pods and spacer placed in a grip pattern as specified in AS2870 (Standards Australia 2011). Steel reinforcement beams where then placed within the spacers between the waffle pods, and a wire mesh placed on the top. The top wire mesh and the reinforcement beam where fastened as required then concrete mix poured and adequately vibrated.

Figure 8. Slab laying - pouring and leveling concrete

The floor was finished by application of a thin top layer of colored cement and sand. The color varied from one room to another as per the plan, for example, a violet floor color was used for the bedrooms.

ii. Brief notes on observables in each of the photographs

Site preparation

· Rumble – waste products from the structures demolished during site preparation

· Heavy duty machinery – excavators used in demolition and earth excavation

· Topography – from the pictures, it is also possible to figure out the generally flat landscape and that it is highly vegetated with trees

· Cleared and leveled site

· Fence

Footing

· Fence

· Excavator

· An excavated strip

· Semi-finished slab – made up of waffle slabs, wire mesh, polythene sheeting, and outside edge boards.

Flooring

· Pier holes

· Excavator fitted with an auger bit attachment

· Top cement layer pouring

· Cement and sand mixture

· Men at work

iii. Hand-drawn sketches of footing and floor system

Figure 9. A sketch of footing and floor system (Adopted from Clarke 2013)

Task 2

Construction sequence for the footing and floor system

Footing

i. First, using the appropriate and available machinery, excavation is done to create a strip.

ii. Steel reinforcement bars are placed in proportion t the expected load and size of the planned structure and the condition of the soil. The reinforcement steel bars are placed in the excavated strip and are elevated slightly using spacers to allow poured concrete to flow beneath.

iii. The footing is done all along the walls, both external and internal, and piers are used to carry the load of the wooden part of the wall.

iv. The footing is then sealed using a high-quality sealer to protect it from moisture (WA Department of Communities 2017).

Waffle slab and floor

v. Efforts are to be made to ensure that the site is adequately leveled as possible. If so required, the site should be cut or filled with sand until adequately level. If the filling is done, then there is to be compact tying to ensure the engineer recommended specifications are attained.

vi. The next step is to carry out termite treatment when chemicals are to be used, then followed by laying of the plumbing system as per plans,

vii. The outside edge boards are then put in place and the area within the edge boards covered with plastic sheeting. At this point, all pipe joints should be checked and taped if so required to avoid any future leaks, as well as moisture absorption into the slab.

viii. A later of wire mesh is then placed followed by placement of the waffle slab pods and spacer, in a grid pattern as pert the footing design requirements (Standards Australia 2011).

ix. Steel reinforcement bars are then placed within the spacer between the waffle slabs,

x. A top layer of wire mesh is laid and fastened adequately to the steel beams as per design specifications. At this point, an engineer should inspect the slab to ensure all standards are met.

xi. After a green light from the engineer, concrete is poured and vibrated effectively to ensure all air bubbles are removed, the ribs are filled fully, and a minimum cover of 25mm and 20mm of cover over the waffle slabs and wire mesh respectively is achieved, or as per engineer specifications (Standards Australia 2011; WA Department of Communities 2017)

Floor surface

xii. When the recommended top concrete layer of the slab is achieved, hand trowel is to be done so as to achieve a smooth floor surface.

xiii. After the surface is adequately cured, after about five days, a waterproofing system is to be applied as per available specifications.

xiv. When all this is done, an inspection request is to be made to the consultant or engineer to approve (WA Department of communities 2017).

Concrete casting requirements

To ensure safe and smooth quality concrete works the requirements below should be observed.

· Before pouring the concrete, the areas which concrete is to be cleared of any dirt, rubbish, and any other deleterious foreign materials through an air compressor machine

· All through the process, the services of a consultant or engineer should be engaged through inspection requests at the various levels, especially for the reinforced steel and concrete pouring.

· In case readymade concrete is used, it should be obtained from a plant approved by the project engineer or consultant.

· Concrete pumps should be on the site, in the right required numbers, and some on standby in case of a breakdown

· At the time concrete is being received or poured, vibrators should be ready

· Delivered concrete should be checked for conformity with design requirements and each truck mixer should be checked for temperature and slump. The temperature should not be more than 30 degree Celsius (Australian Safety and Compensation Council 2008). All this data should be recorded in the daily concrete pour card.

· Once the mix is received and accepted, it is to be poured directly into the concrete pumps and adequate care taken to ensure that during pouring, it is not more than 2 meters.

· For the footing, vibration should be done at every 400mm until the top level is attained.

· Safety procedure and instructions must be observed at all levels including protective wear for all workers, experts operating machinery, etc (Australian safety compensation council 2008).

Task 3

Soil classification

According to Australian building standards, knowledge of the soil is essential when building a structure. Essential features of the soil include chemical and physical properties, stability, deformation when wet, depth of the bedrock, and corrosiveness.

The current site is classified as an abnormal site because it had existing structures which had to be removed during site preparation and the presence of tree on the adjacent site. The presence of a structure affects the moisture content of the soil, and tree in the neighboring plots has a footprint on the site. The site is located in Sydney; it has black clay soil which is determined to be class S and slightly reactive (Isbell 2016).

Figure 10. Soil classification - black soil class S

Suitability of the footing and floor system

The building’s footing system is founded on a better and stiff clay soil well below the topsoil, deleterious, slope wash soils of uncontrolled fill. The footing of the entire structure is on strata with similar features thus minimizing the risk if differential movements and articulation is provided as required (Charman and Murphy 2007).

The slab-on-ground has been laid with pad footings and edge beams which provide support for concentrated loads (Prescott 1931). The footing system has been laid in accordance with principles and guidelines provided by engineers and are proportioned along the entire structure to ensure equal and even load distribution. The footing system has both steel reinforcement and piers that are founded well enough into the ground and proportioned to bear a pressure load of 500kPa.

The floor system is laid with waffle raft slab which is one of the strongest forms of slab. This form of floor has closely spaced grid of 110 with ribs at 1090mm maximum with the center in either direction. 150×300 edge beams have been used with expanded polystyrene block that is laid with spacers. The spacers have been reinforced with steel beams which further strengthens the slab (Charman and Murphy 2007; Standards Australia 2011). A slab-on-ground type of slab has been used and this helps to do away with the excavation of a trench which has the potential to compromise the footing, slab, or basement walls by groundwater absorption. Precast waffle slabs use N high strength steel bars and not mesh, it’s made with standard fabric for slabs, and it is 85 thick which is required for class S sites.

Task 4

The current building uses a solid ground concrete floor system. One of the other possible alternatives is the use of suspended timber floor. A suspended timber floor is usually constructed using timber joists suspended from bearing walls, which are then covered with either floorboards or some other form of boarding material. The joists are typically laid across the shortest span. Concrete floor and suspended timber floor compare diversely across various parameters.

Construction process

A suspended timber floor system, just as the name suggests is made of timber joists which are suspended from bearing walls. The floor is then covered using floorboards. The joists are normally positioned across the shortest possible span. On the other hand, solid ground cement floor used in the structure is made of different materials and parts. The top layer is made of concrete, it is level, and contain a floor screed (Thomas and Ding 2018).

Installation of services

The services installed in a floor system include sewer, stormwater, heating, gas, and water. In both cement and timber floor systems, installation of these services is done when the floor is set up. In a cement floor, services are installed after the ground is compacted and treated for termite protection. On the other hand, in timber floor, services are installed within the sand/cement mix above the sterling board. The laid down plan should be observed when installing services and the flooring of every pipe well checked to avoid leaks (Standards Australia 2013).

Termite protection

Several termite protection strategies are used in cement floor including minimized construction breaks, termite treatment using chemicals, and footing and slab designed to prevent termite entry. For timber floor system, termite treatment is more critical and it starts with the treatment of the timber used for the floor and the use of termite shields or caps (Ewart 2001). These are however not deemed to be primary termite prevention strategies, but rather as facilitators to inspection exercise (Building Development 2016).

Insulation properties

For a suspended floor system, insulation is done using boards or batts which are added between the joists. This requires that the insulation is cut and installed effectively to tightly fit in between the joists. The aim of the tight installation is to ensure there are no gaps which allow air movement and thus, heat loss (Pelsmakers and Elwell 2017). On the other hand, insulation for the concrete floor is done when the slab is being laid. Polythene insulation is placed on the slab, which also acts as a vapor barrier.

Sustainability/environmental impact

Timber used in a timber floor means cutting trees down thus its counter-intuitive, but from a critical point of view, timber floor system has far less impact on the environment as compared to the concrete floor system. Timber is renewable, and the effect of cutting down trees is overcome by using trees from plantation grown for the purpose of construction timber. On the other hand, concrete floor system requires steel, cement, and many other materials which require industrial processing. These in aggregate have a wider impact on the environment (Ortiz et al. 2009)

Cost

The costs involved in building a concrete slab are very high. These costs range from the materials, the labor, and the time invested. Some of the materials required to build a concrete floor are the formwork, steel reinforcement beams, pump and vibrator, and costs for the flooring finish. On the other hand, timber floor system is easier to install. Only a carpenter is required, it can be created on site, and it is even more flexible in case of renovations in the future (Smith et al. 2009). Timber flooring system is certainly the best option for homeowners on a budget.