Geotechnical tests

The geotechnical laboratory tests evaluated the properties of concrete, masonry and blend. The tests procedure are the same in use for natural aggregates and soils. The tests were performed in the geotechnical laboratory of University of KwaZulu Natal (UKZN) with the exception of Los Angeles Abrasion test, which was carried out in the laboratory of the eThekwini Municipality, and the Durability Mill Index in the Soilco Materials Investigations (Pty) Limited laboratory in Pinetown. All results obtained were compared with the limits suggested by the COLTO classification attached in Appendix B.

4.2.3.3.1 Determination of specify gravity and water absorption

Specific gravity and water absorption of materials were determined following the test methods TMH1-B14 and SANS 3001-AG21:2011. Different test procedures are used for the fractions larger and finer than 4.75mm. Water absorption is one of the main characteristics of C&D material that affects the amount of water necessary for compaction and the durability.

4.2.3.3.2 Particle size distribution analysis

The C&D waste aggregates were prepared during the crushing, screening and mixing procedure as shown in Figure 2 to fall within G1-2-3 grading envelope of COLTO.

4.2.3.3.3 Atterberg Limits

The liquid limit, plastic limit and plasticity index were determined through methods A2 and A3 of the THM1. This group of tests investigates the plasticity of the materials passing 0.425 mm.

4.2.3.3.4 Compaction test

The TMH1 compaction test method-A7 was followed on specimens with particle size smaller than 19mm using a modified methodology developed by the AASHTO for determining the bearing characteristics of the typical Class 2 aggregate base (Theyse, 2002)

4.2.3.3.5 Californian Bearing Ratio (CBR)

The California Bearing Ratio (CBR) test was also performed on the materials passing the 19mm sieve. Specimens were compacted at OMC using varying compactive efforts as suggested by TMH1 and were tested in soaked condition. The CBR value, which indicates the strength of a material, was interpolated for 98% modified AASHTO density, by determining the bearing ratios at the different densities.

4.2.3.3.6 Flakiness Index

The flakiness index of coarse aggregate is used to determine the percentage of flaky aggregates. The spherical shape of an aggregate allows obtaining an appropriate packing

without applying excessive energy in compaction. In accordance to South African standard, the test is performed on three different size ranges.

4.2.3.3.7 Durability Tests

A series of durability tests have been performed. These are not only important for the South African classification, but for the applicability and workability of C&D waste materials in general. In fact these tests describe the ability of the aggregates to withstand the environmental and mechanical degradation during construction and service period of the aggregates. The tests are split in two typologies for simulating the mechanical stress and weathering behaviour.

Los Angeles Abrasion (LAA) test and Durability Mill Index (DMI) assess the durability of materials by means of its abrasion, Aggregate Crushing Value (ACV) considers strength aspect.

The universally recognised LAA test is the most common test to evaluate toughness, strength and abrasion characteristics. In Europe is largely use and it has a proper limits for natural and C&D materials. This test followed the South African specification SABS 846 although it is not a requirement of COLTO for sub-layerworks.

The standard South African tests for assessing the durability of an aggregate are the 10 per cent Fines Aggregate Crushing Value (10% FACT) and ACV for G1 G2 or G3 materials, while DMI is used for G4 materials. The inability to perform the test 10% FACT due to limited sample available sizes led to the use of the related test, the Aggregate Crushing Value (ACV), which also defines the strength. The two tests have a direct correlation when ACV is between 14 and 30 and the 10%FACT range from 300 to 100 kN (Alexander and Mindess, 2005).

ACV = 38 – 0.08 x 10% FACT

The ACV test followed the specification included in TMH1 method B1 which assesses the behaviour of the aggregates under compression in dry or wet conditions.

The Durability Mill Index (DMI) follows the recommendation of Sampson and Roux (1987). In this non-standard abrasion test the sample is split in 4 sub-samples, named A, B, C, and D based on the size of the aggregates. Sub-sample A is prepared in order to determine the plasticity indexes by means of the Atterberg’s methodology. The abrasive resistance of the remaining sub-samples is investigated under wet and dry conditions inside the Durability Test Machine. As shown in Figure 4-5, the testing equipment is similar to the more common LA Abrasion Test Machine.

 

For a better understanding of the C&D waste durability properties in long term due to weathering conditions, a modified ACV was performed, with the samples undergoing ten wet- dry cycles. Each cycle took 24 hours, 17 hours for the sample to be kept in soaked condition and 7 hours in an oven at 60°C as suggested by Pennsylvania PA test method no 519.

4.2.3.3.8 Consolidated Drained Triaxial Test

Consolidated drained (CD) triaxial tests were carried out on samples of blend material so as to complete its geotechnical characterization. These tests were carried out to obtain the shear strength characteristics of the material which are required for the analysis of slopes in view of its practical applications for road construction. Angle of friction and cohesion are calculated and compare with the standard classified granular material used in South African road pavements.

The blend material was sieved and the maximum particles dimension was set to 19 mm as for other tests. This enabled the triaxial sample size of 100 mm diameter and 200 mm length to have an acceptable ratio of maximum size of aggregates to specimen diameter ratio close to 1/5. The specimen was prepared at compaction equal to 100% of modified AASTHO and then saturated.

4.3 Results and discussions