Module Learning Outcomes
After the successful completion of this exercise you will be able to:
- Acquire laboratory data at an appropriate level of accuracy and interpret it in terms of underlying engineering principles.
- Present relevant information and analysis in a clear and unambiguous way. These are module learning outcomes 3 and 5 which are common to both modules.6. Aims and objectives
The specific aim of this coursework is to undertake an investigation to validate the theory associated with concrete mix design and the use of Pulverised Fly Ash (PFA) as a partial cement replacement, and Self-Compacting Concrete (SCC). The objectives are:
1. Design a SCC trial mix using the BRE method as a basis, with PFA as a partial cement replacement and to provide a 500 kg/m3 cementitious powder content, with super plasticiser and viscosity modifying admixtures.
2. Assess whether workability tests have been conducted in accordance with standard test methods and assess the significance of the results.
3. Perform standard tests on samples to determine the mechanical properties of the hardened concrete.
4. Re-design the trial mix using the observed workability and strength results.
5. Assess the embodied carbon of the trial mix using the Inventory of Carbon and Energy database.
6. Research and discuss the efficacy of using PFA as a partial cement replacement and self-compacting concrete to improve the sustainable use of concrete in practice.
7. Procedure
It is not necessary to re-attend the laboratory sessions for this resit coursework. Use the data provided in this report to complete your investigation.
Trial mix design
Design a 0.05 m3 trial mix to the following specification:
Characteristic strength: C32/40
Test age1: 28 days
Percentage defectives: 5%
Slump: 100 mm
Slump flow: 800 mm (but use your target slump for the design process)
Cement: CEM1 class 42.5
Coarse aggregate: 20 mm maximum size, crushed Fine aggregate: 70% passing 600 μm sieve
Notes:
The mix should be designed to have a powder content of at least 500 kg/m3. This may require the use of PFA, which may be assumed to develop 30% of the strength of an equivalent mass of cement (i.e. C+0.3F), up to a maximum proportion of 40% PFA. Any PFA content in excess of 40% should be assumed to not contribute to the strength and is merely acting as an inert mineral filler, which may require the cement content to be increased in order to achieve the required strength.
Concrete Casting
During mixing an additional 0.5 litres of water was added. The mix achieved a slump of 80 mm when tested to BS EN 12350-2:2009 Testing Fresh Concrete, Part 2: Slump test. During the slump test both layers of concrete were tamped 25 times.
The following admixtures were then added to the mix:
- V-MAR 6 manufactured by Grace Construction Products
- Conplast SP430 manufactured by FOSROC
From the manufacturers product information leaflets, available on the module web, determine the appropriate minimum-range amount of these admixtures that should have been initially added to the mix in order to try to achieve the desired SCC. On inspection of the concrete mix during the mixing testing it was decided to add an additional 20% of the minimum amount of super plasticiser.
The workability of the SCC mix was then measured using:
Slump flow (BS EN 12350-8:2010 Testing Fresh Concrete, Part 8: Self-compacting concrete - Slump flow test) V-funnel (BS EN 12350-9:2010 Testing Fresh Concrete, Part 9: Self-compacting concrete - V-funnel test)
L-box (BS EN 12350-10:2010 Testing Fresh Concrete, Part 10: Self-compacting concrete - L-box test) The results obtained are recorded in Appendix A:
During the V-funnel test the gate was opened about 30 s after the funnel had been filled with concrete. During the L-box test there was some sign of segregation of the mix.
The following concrete test samples were produced: 3 No. 150 mm cubes 3 No. 100 mm diameter, by 200 mm long cylinders 24 hours after casting the samples were placed in a curing tank and left underwater until being tested at 28-days.
Concrete Testing
The results table in Appendix A contains the mass of each sample prior to testing and the maximum compressive load applied.
The Report Results
Do not quote results without explaining how they have been obtained by showing typical calculations for at least one result (and then tabulate the rest for similar samples).
For the casting and sample testing:
- Present the trial mix design.
- Present the results for the slump flow and passing ability ratio.
- Present the results for the concrete sample density and compressive strength.
- Determine the characteristic strength of the concrete trial mix from the samples tested.
Discussion
For the casting and sample testing:
- Review the description and notes in the sample casting section and discuss the validity of the experimental results.
- Critically assess whether the trial mix achieved the specification and is suitable for use as a SCC. Cite and compare all of the appropriate results (and assumptions given your assessment of the validity of the results) to justify your decision.
For the mix re-design:
- Re-design the mix in order to achieve the design specification - adjust the trial mix proportions to achieve the target slump, characteristic strength and expected density. Do not forget to include the effect of any changes to the w/c ratio made by changing the water content during mixing.
- Suggest new quantities for admixtures in order to achieve the SCC workability specification. You should explain your mix re-design methodology and procedure in this section of the discussion.
For the sustainability assessment:
- Using data from the "Inventory of Carbon and Energy" (see module web) determine the embodied carbon per kg of your blended cement, and SCC mix, and compare them to the values you would expect for a non-SCC mix which did not use a PFA cement replacement but had similar strength performance. Hence explain what these results show regarding the use of PFA as a cement replacement material, and the use of SCC, for sustainable construction practice. Cite other reference sources and pertinent information as required to justify your answer.