Materials Technical Report Essay Examples & Outline

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Concrete Materials Technical Report


Summary

This technical report presents the findings of concrete tests done with samples casted using PFA as a partial replacement for cement. The samples exhibited good mechanical properties desired for structural concrete, in addition to improving some of the concrete properties. The characteristic strengths of the samples containing PFA are exceptionally high and can be used in structural design.

Introduction

Well cured and hardened concrete material has to be strong enough in order to be able to withstand all the structural and service loads intended to be applied to it. It must also be sufficiently durable to withstand the environmental conditions for which the structure is designed. Using high quality materials that are well mix-designed, handled and well placed and finished ensures that the concrete material produced attains high strength and becomes durable when used in structural building (Dhir, et al., 2002).

Properties of hardened concrete include: workability, creep, shrinkage, water tightness, strength and rate of strength gain, durability, and Modulus of Elasticity. These concrete properties depend on the mix design (mix proportions), the curing conditions and the environment (Shirley, et al., 2009). Concrete strength generally refer to its compressive strength, because concrete is very strong in compression and relatively weak in tension. Concrete compressive strength largely depends on the amount of cement used, the water-cement ratio, aggregates, curing conditions, age, and admixtures used (Thomas, 2007).

A lot of research has been ongoing to address some deficiencies of concrete, with some providing very significant efforts geared towards improving its structural performance. The existing literature shows that partial replacement of cement using mineral admixtures can significantly reduce the porosity and improve the density and durability of concrete, alongside improving the compressive strength, flexure and tensile strength. A part from enhancing concrete’s ability to exhibit greater resistance against harmful chemical attack and environmental conditions, mineral admixtures significantly contribute to sustainable environment as partial replacement of Portland cement and are normally referred to as “ less energy intensive” cementitous materials (Thomas, 2007).

Among available mineral admixtures, the most commonly used are pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS), silica fume (SF), rice husk ash (RHA) and metakaolin (MK) (Khatib, 2009). PFA has also worked well and recommended for structural use as a partial replacement of fine aggregate. This report presents the results obtained for density, compressive strength test and RC beam test for Self compacting concrete (SCC) samples tested using standard methods. The concrete cubes and cylinders were prepared by designing and batching a concrete mix using Pulverized Fly Ash (PFA) as a partial replacement of cement.

Experimental Method

Initially, 0.035 m3 of concrete trial mix was designed using the BRE method to the specifications on page 2 and 3 of the lab manual for a test age of 28 days. VMA compounds and super plasticizer were added to the concrete sample to produce the SCC mix. From this mix, 3 concrete cubes were prepared using cubical molds with a length of 100mm, and another 3 cylindrical concrete samples were prepared using cylindrical molds 100mm diameter and 200mm long.

The masses of hardened concrete samples were measured and then the cubes tested for compressive strength using the Schmidt rebound hammer after the 28 day period of curing under a tank of water. An ultrasound of equipment was used to determine the value of elastic modulus of the concrete, and hence, its compressive strength as well. The samples were then tested for compressive strength using a destructive method under increasing load, and the maximum load at failure and the modes of failure recorded. Reinforced concrete (RC) beam was prepared by making a reinforcement cage to the bar schedule drawing in the lab and then placing it in a reinforced concrete mold measuring 1.5m by 100mm by 200mm. The beam was set as shown in the figure below.

After setting the beam, demec and deflection readings for zero load were recorded. The positions of the demec points were then measured and recorded, ensuring that the load was applied at 1/3rd beam span positions and deflections measured at mid-span. The beam was loaded in load increments of 3kN up to 30kN, recording demec and deflection readings at every load increment. After 30kN, the load increment was reduced to 1 kN and only deflection was measured. When deflection began to show large increases, the deflection gauge was removed and the beam loaded to failure and the failure load and mode of failure recorded.

Results

Cubes
Cube 1
Dimensions: 100mm X 100mm
Area = 10000mm2
Mass of cube in air = 2351.5g
Mass of water before placing cube = 1318.6g
Mass of water after placing cube = 33.6g
Mass of water displaced = (1318.6 – 33.6) = 1285g
Volume of water displaced = 1285cm3
Density of the cube = = 1.830g/cm3
Cube maximum load = 517.10 kN
Cube compressive strength =
Modulus of elasticity (E) =
Where:
= density of concrete (kg/m3)
= compressive strength of concrete (MPa)
E = = 18.58 GPa
Ultrasonic pulse rate =

The densities for cube 2 and 3 were calculated using the steps above and the results presented in table 1 below:

Table 1: Cubes

Cube Mass in air (g) Mass of water before placing cube(g) Mass of water after placing cube(g) Volume of water displaced(cm3) Density of cube(g/cm3) Cube maximum load(kN) Cube compressive strength (N/mm2) Ultrasonic pulse time(s) Modulus of elasticity, E(GPa)
1 2351.5 1318.6 33.6 1285 1.830 517.10 51.71 21.6 18.58
2 2366.1 1325.0 33.5 1291.6 1.832 491.84 49.18 22.0 18.15
3 2303.0 1284.9 33.6 1251.3 1.840 514.24 51.42 21.5 18.68

Mean compressive strength of the 3 cubes = 50.77 kN
Mean modulus of elasticity for the 3 cubes = 18.47

Cylindrical concrete samples
Dimensions: Diameter 100mm, Length = 200mm
Area = () = = 7853.98mm2

Cylinder Mass in air (g) Mass of water before placing cube(g) Mass of water after placing cube(g) Volume of water displaced(cm3) Density of cube(g/cm3) Cube maximum load(kN) Cube compressive strength (N/mm2) Modulus of elasticity, E(GPa)
1 3666.0 2070.7 33.6 2037.1 1.799 337 42.91 16.49
2 3680.7 2080.7 33.6 2047.1 1.797 362.52 46.16 17.08
3 3682.8 2081.6 33.6 2048.0 1.798 248 31.58 14.14

Table 2: Cylindrical concrete samplesRC Beam Testing Results

Modulus of elasticity
d = h-23mm
d = 200-23 = 177mm
h = 200mm
As = 200 x 100mm
Cube maximum load = 72.53 kN
Cube compressive strength =
Modulus of elasticity (E) = =
The mean compressive strength of the 3 cubes = 50.77 kN, so the mean static modulus is Ec is 34.
Modular ratio (m) = = =
Replacing the values of b, y, m, As and D in the equation b.y.(y/2) = m.As(d-y) and solving the resulting quadratic equation, the value of y = 176.99mm.
Maximum load = 72.53kN
Stress =

The table below shows the results for the RC beam test performed

Load(kN) Stress Deflection(mm) Demec readings(
0 0 0 1 2 3 4 5
3 10.0 0.28 2.096 2.050 2.064 3.238 2.701
6 20.0 0.49 2.035 1.997 2.015 3.195 2.659
9 30.0 0.71 2.024 2.038 2.059 3.245 2.713
12 40.0 0.96 2.063 2.040 2.066 3.262 2.732
15 50.0 1.25 2.051 2.039 2.074 3.282 2.765
18 60.0 1.60 2.033 2.039 2.088 3.309 2.803
21 70.0 1.88 1.990 2.016 2.081 3.321 2.834
24 80.0 2.17 1.969 2.008 2.083 3.337 2.860
27 90.0 2.45 2.057 2.111 2.198 3.464 3.002
30 100.0 2.70 1.953 2.024 2.119 3.406 2.965
31 103.3 2.84 1.938 2.013 2.118 3.410 2.966
32 106.7 2.91
33 110.0 2.90
34 113.3 3.07
35 116.7 3.18

Discussion

Elastic modulus is one of a key factor in determination of deformation of a structural element and modular ratio used in the design of members subjected to flexure. A higher value of E means that the concrete is good enough to withstand a relatively high elasticity. The typical modulus of elasticity for normal concrete is around 17GPa, while for high strength concrete, it is around 30GPa (Ramezanianpour, 2013). Concrete cubes have a relatively higher modulus of elasticity compared to concrete cylinders. High modulus of elasticity is suitable for concrete since it should be strong enough to carry all the desired loads in compression.

The strength exhibited by the samples tested is within the acceptable range of design expectation as of those where the PFA is not used. The use of PFA in structural concrete has both economic and technical benefits. It reduces permeability and produces a cohesive concrete matrix that has reduced rate of bleeding, and can self-compact (Gingos & Mohamed Sutan, 2011). The long term strength, durability and performance of the concrete are some of the great properties achieved when fly ash is used as a partial replacement for cement. Based on the proportion of PFA in the concrete mix, a significant reduction of concrete carbon footprint can be achieved.

Read more about material rate of strain vs Stress

Conclusions

The use of PFA as partial replacement of cement does not significantly affect the mechanical properties of concrete, including its characteristic strength. The admixture also improves some of the properties of concrete such as reduction in permeability, shrinkage, creep and resistance to chemical attack. PFA should therefore incorporated in Portland cement as a partial replacement for the cement because of its environmental benefits as well as suitability in structural concrete.

References

Dhir, R. K., Hewlett, P. C. & Csetenyi, L. J., 2002. Innovations and Developments in Concrete Materials and Construction: Proceedings of the International Conference Held at the University of Dundee, Scotland, UK on 9-11 September 2002. UK, Thomas Telford.
Gingos, G. & Mohamed Sutan, N., 2011. Effect of PFA on Strength and Water Absorption of Mortar. UNIMAS e-Journal of Civil Engineering, 2(1), pp. 7-10.
Khatib, J., 2009. Sustainability of Construction Materials. Amsterdam: Elsevier.
Ramezanianpour, A. A., 2013. Cement Replacement Materials: Properties, Durability, Sustainability. New York: Springer Science & Business Media.
Shirley, R., Claisse, P. & Ganjian, E., 2009. Properties of concrete using high-limepfa from a UK source. Proceedings of the ICE - Construction Materials. UK, ICE Publishing.
Siddique, R., 2007. Waste Materials and By-Products in Concrete. New York: Springer Science & Business Media.
Thomas, M., 2007. Optimizing the Use of Fly Ash in Concrete.