‘Aggregate’ is a collective term for mineral materials such as sand, gravel, ballast and crushed stone that are used with a binding medium to form compound materials i.e. Asphalt concrete and cement concrete. Coarse aggregate occupies almost 50–80% by weight of concrete. As such, its performance has a significant influence on strength and durability of concrete. Los Angeles Abrasion (LAA) is the most popular field test for performance evaluation for aggregates. This test provides value of the strength characteristics of aggregates that is closer to the actual material breaking condition in the process of mixing, unloading and compaction, thereby making it an indispensable field test for performance evaluation. However, several studies have reported that for some aggregates, despite having a great LAA value, their strength and stability is poor, consequent to their morphology.
In fact, morphological features of aggregates, such as; contour shape, angularity and surface texture, have been proven to affect various aspects of strength and ultimately the performance of coarse aggregates. Unfortunately, majority of the previous studies investigating morphology of aggregates have mainly focused on the shape, volume, and surface properties of aggregates only, paying little attention to the morphology decay law of aggregates during the application process.
In this view, Chang’an University researchers: Dr. Haitao Ge, Pro. Aimin Sha, Dr. Zhenqiang Han, Dr. Xiaowei Xiong focused on the accurate characterization of all morphological characteristics of coarse aggregate with the objective of providing a more accurate and comprehensive performance evaluation and forecast technique for aggregates in engineering. In particular, they applied 3D laser scanning techniques as opposed to X-ray CT scan previously used. Their work is currently published in the research journal, Construction and Building Materials.
The authors used a 3D laser scanner to obtain three-dimensional points cloud data of aggregate particles that had been subjected to 0, 500, 1000 and 2000 abrasion cycles. Afterwards, the researchers processed the data using a software of reverse engineering based on morphology evaluation indexes. Eventually, the minimum bounding box algorithm was developed to calculate flat-elongated index and it helped illustrate the morphological characteristics of coarse aggregate particles with different size and abrasion cycles exposure.
It was observed that aggregates with small size had bigger quantity proportion of elongated particle. Also, they noted that the greater the angularity of aggregates was, the faster their angular decay rate. Moreover, aggregate particles with small size were seen to have a richer surface texture which was easy to lose when subjected to abrasion process. The researchers also found out that sphericity index increased, while specific surface area and flat-elongated index presented a downward trend as the particle size became bigger for different abrasion cycles.
In summary, their study demonstrated the characterization of shape properties of coarse aggregates with the objective being to quantitatively evaluate morphological characteristics and abrasion decay laws of coarse aggregate, so as to make an accurate performance evaluation for aggregates. Consequent to the inadequacies of LAA to capture performance of aggregates, this novel approach has been devised. Altogether, the indexes proposed in the study were able to characterize different aspects of coarse aggregates morphological property, and it is beneficial for the evaluation and selection of aggregates used in engineering construction.
Haitao Ge, Aimin Sha, Zhenqiang Han, Xiaowei Xiong. Three-dimensional characterization of morphology and abrasion decay laws for coarse aggregates. Construction and Building Materials, volume 188 (2018) page 58–67.Go To Construction and Building Materials