What is Marshall Mix Design for Bituminous Materials?

The Marshall Mix Design method was originally developed by Bruce Marshall of the Mississippi Highway Department in 1939. The main idea of the Marshall Mix Design method involves the selection of the asphalt binder content with a suitable density which satisfies minimum stability and range of flow values.

The Marshall Mix Design method consists mainly of the following steps:

(i) Determination of physical properties, size and gradation of aggregates.

(ii) Selection of types of asphalt binder.

(iii) Prepare initial samples, each with different asphalt binder content.
For example, three samples are made each at 4.5, 5.0, 5.5, 6.0 and 6.5 percent asphalt by dry weight for a total of 15 samples. There should be at least two samples above and two below the estimated optimum asphalt content.

(iv) Plot the following graphs:

(a) Asphalt binder content vs. density
(b) Asphalt binder content vs. Marshall stability
(c) Asphalt binder content vs. flow
(d) Asphalt binder content vs. air voids
(e) Asphalt binder content vs. voids in mineral aggregates
(f) Asphalt binder content vs voids filled with asphalt

(v) Determine the asphalt binder content which corresponds to the air void content of 4 percent

(vi) Determine properties at this optimum asphalt binder content by reference with the graphs. Compare each of these values against design requirements and if all comply with design requirements, then the selected optimum asphalt binder content is acceptable. Otherwise, the mixture should be redesigned.

marshall-mix-design

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

What is the principle of Asphalt Mix Design?

The main objective of asphalt mix design is to achieve a mix with economical blending of aggregates with asphalt to achieve the following :

(i) workability to facilitate easy placement of bituminous materials without experiencing segregation;
(ii) sufficient stability so that under traffic loads the pavement will not undergo distortion and displacement;
(iii) durability by having sufficient asphalt;
(iv) sufficient air voids

In asphalt mix design, high durability is usually obtained at the expense of low stability. Hence, a balance has to be stricken between the durability and stability requirements.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

10 Things to Remember when doing Concrete Mix Design

Good quality concrete starts with the quality of materials, cost effective designs is actually a by-product of selecting the best quality material and good construction practices. Following are 10 Things to remember during Concrete Mix Design and Concrete Trials.

1. ACI and other standards only serves as a guide, initial designs must be confirmed by laboratory trial and plant trial, adjustments on the design shall be done during trial mixes. Initial design “on paper” is never the final design.

2. Always carry out trial mixes using the materials for actual use.

3. Carry out 2 or 3 design variations for every design target.

4. Consider always the factor of safety, (1.125, 1.2, 1.25, 1.3 X target strength)

5. Before proceeding to plant trials, always confirm the source of materials to be the same as the one used in the laboratory trials.

6. Check calibration of batching plant.

7. Carry out full tests of fresh concrete at the batching plant, specially the air content and yield which is very important in commercial batching plants.

8. Correct quality control procedures at the plant will prevent future concrete problems.

9. Follow admixture recommendations from your supplier

10. Check and verify strength development, most critical stage is the 3 and 7 days strength.

Important note:
Technical knowledge is an advantage for batching plant staff, even if you have good concrete design but uncommon or wrong procedures are practiced it will eventually result to failures.

We at engineeringcivil.com are thankful to Tumi J. Mbaiwa for submitting these 10 points which are helpful to each and every civil engineer.

Filed under Mix Design | 1 Comment

Cement And Water Saving With Water Reducers

By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

In India 0.93 kg of CO2 is emitted in the production of one kg of cement. In the financial year 2009-10 India produces 200 million tonnes of cement. In the production of this cement 186 million tonnes of CO2 was emitted in the atmosphere during financial year of 2009-10.

The availability of water in India per person per year in 1950 was 5177 cu.m. In the year 2009 it is reduces to 1700 cu.m.

If 50 million tonnes cement in making concrete uses water reducers 7500000 tonnes of cement can be saved. 3750000 kl of potable water will be saved and the saving of Rs. 3300 crores per year to construction industry. This amount is worked out after adjusting the cost of water reducers. Less cement used means less cement required to be produce by the cement factories resulting 6975000 tonnes of CO2 will be prevented to be emitted to the atmosphere. These are worked out with an average saving of 15% cement and 15% water.

CO2 emission is word problem, but for India in addition to CO2 it has problems of Air, Water, Soil, Food and Noise pollutions. Less densily populated countries may cope with these problems but for India it is of the top concern. The population figures of 2009 is, India 350 person per sq.km, China 132 person per sq.km and USA only 34 person per sq.km. The figures of 2006 CO¬2 emissions are USA 658.60 tonnes per sq.km, China 611.76 tonnes per sq.km and India 459.35 tonnes per sq.km. Every one should contribute his or her efforts to save the environment from pollution. Those involve in the construction activities can contribute their share by proper design of concrete Mixes. This is best illustrated by the following examples.
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Concrete Mix Design – M70 Grade of Concrete (OPC 53 Grade)

Concrete mix design – M70 grade of concrete provided here is for reference purpose only. Actual site conditions vary and thus this should be adjusted as per the location and other factors.

A. Design Stipulation:
Characteristic comprehensive Strength @ 28 days = 70 N/mm2
Maximum size of aggregate = 20 mm
Degree of workability = Collapsible
Degree of quality control = Good
Type of exposure = Severe
Minimum cement content as per is 456-2000

B. Test data for concrete ingredients
Specific gravity of cement = 3.15
Specific gravity of fly ash = 2.24
Specific gravity of microsilica = 2.21
Setting time of cement initial = 165 min, final = 270min
Cement compressive strength =
39.0 N/mm2 @ 3 days
51.0 N/mm2 @ 7 days
64.2 N/mm2 @ 28 days
Specific gravity of coarse aggregates (ca) and fine aggregates (fa)
20 mm 2.729
10 mm 2.747
R/sand 2.751
C/sand 2.697

Water absorption
20 mm 1.540, 10mm 1.780, R/sand 3.780, C/sand 4.490

Characteristic strength @ 28 days 70 N/mm2
Target mean strength : Depend upon degree of quality control “good” and considering (std. Dev.As 5 N/mm2)

Characteristic strength given by the relation 70 +(1.65 *5 ) = 78.25 N/mm2

C. Quantities of ingredients (By Absolute Volume Method )
Actual cement used = 486 kg/cum
Actual fly ash used = 90 kg/cum
Actual microsilica used = 24 kg/cum
W/C fixed = 0.26
Absolute volume of cement = 0.154
Absolute volume of air = 0.02
Absolute vol of water. = 0.156
Absolute vol of fly ash. = 0.040
Absolute vol of microsilica = 0.011

Total volume of CA and FA used = 1.00-(0.155+0.044+0.022+0.02 +0.154)
= 0.619 Cum

D. Aggregate percent used.
20 Mm = 24, 10 mm = 36, r/sand = 20, c/sand = 20

(2.729*0.24) + (2.747*0.36) +(2.751* 0.20 )+(2.697*0.20) *0.619*1000
405+612+340+334=1691

Aggt: cement = 2.82 : 1

Mix proportion = 0.26:1:0.57:0.56:1.02:0.67

E. Abstract:
20 mm = 405 kg/cum
10 mm = 612 kg/cum
r/sand = 340 kg /cum
c/sand = 334 kg/cum
water = 154 kg/cum

Admixture 0.50 % BY WT OF (C+F+MS) ASTP-1 OF BASF

Cube Compressive Strength (N/mm2)
3 days = 49.13
7 Days = 59.57
28 Days = 81.49

Note: Mix design is same for Crane bucket and Pump concrete only admixture dosage will fine tuned by 0.05 to 0.10%
We are thankful to Deshmukh D S for submitting this very useful mix design information to us.

Filed under Mix Design | 9 Comments
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