Degradation mechanism and life prediction of tailings and waste rock aggregate geopolymer concrete under freeze-thaw corrosion

To study the durability of tailings and waste rock aggregate geopolymer concrete (TWGPC), a large number of tailings and waste rock were used to replace natural sand and stone as aggregates, and a fly ash geopolymer was used to replace cement as cementing material to prepare TWGPC. The slow freezing method was used to carry out single freeze-thaw and freeze-thaw corrosion tests. Scanning electron microscopy and energy dispersive spectroscopy (SEM–EDS) were used to analyse the microstructure and reaction products of TWGPC. The degradation mechanism of TWGPC was studied, and the life of TWGPC was predicted. The results show that the higher the concentration of corrosion solution was, the more significant the change trend of the mechanical properties test results. In the early stage of the cycle, acinar gypsum and short columnar ettringite were generated to fill the pores and improve the compactness and frost resistance of TWGPC. In the late stage of the cycle: calcium-silicate-hydrate (C-S-H) was decomposed and gradually replaced by magnesium-silicate-hydrate (M-S-H). The cohesion between mortar and aggregate was reduced, and a large number of products were generated. Cl- inhibited the transmission rate of SO42- and reduced the erosion effect of SO42- on TWGPC. The single freezing-thawing life prediction model had high accuracy, and the life prediction conclusion based on reliability was consistent with the appearance damage analysis, mechanical property testing and microscopic morphology analysis.

Cement-Treated Volcanic Scoria for Low-Traffic Road Pavements in the Azores Archipelago

The Azoreans rely on an extensive network of rural roads for the most of the rural population’s activities (primary sector) and accessibility. To rehabilitate and maintain this network, asphalt concrete and crushed rock aggregate are usually used. However, in the region, the application of such paving technology can be extremely costly. It requires specialized contractors, dedicated equipment and raw materials that must be imported to most of the islands. Therefore, the use of locally available materials would result in more flexibility and fewer costs for planned interventions. In the Azores, known as bagacina, the volcanic scoria is a pyroclastic material, generally highly abundant in volcanic islands. This natural aggregate is inexpensive, easy to extract, and presents good geotechnical characteristics. However, due to its porous nature, it generally does not comply with the current specifications for pavement materials. Therefore, this study aims to evaluate cement-treated volcanic scoria to be used as low-traffic road pavement layers. The geotechnical properties and mechanical performance of the two types of scoriae were analyzed. As a result, both types of scoriae presented good behavior, according to the expected for a cement-treated material, and proved to be a suitable alternative for road pavements in the Azores Archipelago.

The variability in commercial laboratory aggregate testing for road construction in South Africa

Simple data comparisons were undertaken using project data to illustrate the need for duplicate test analyses in road construction material investigations for hard rock aggregate sources. Test data was sourced from projects commissioned by the South African National Roads Agency SOC Limited (SANRAL). All test results except the polished stone value were reported by commercial geotechnical laboratories that are accredited with the South African National Accreditation System (SANAS). Only samples subjected to duplicate test analyses were used, as this method allows direct comparisons. The tests used for comparison included the polished stone value, wet and dry versions of the Aggregate Crushing Value test, wet and dry versions of the 10% Fines Aggregate Crushing Value test, the ethylene glycol-soaked version of the 10% Fines Aggregate Crushing Value test, and the water absorption test of both the fine (-5.00 mm) and coarse (+5.00 mm) material fractions. The results show that duplicate testing is firmly justified, as test results reported were often highly variable, despite all participating laboratories being SANAS-accredited and using standardised methods. Further consideration was then given to the additional cost of duplicate testing at project stage investigations compared to the cost implications of having erroneously reported materials failing in service or having good-quality materials rejected.

Study on the adhesion performance of medium weathered igneous rock aggregate and asphalt

In view of the current situation of the shortage of alkaline aggregate and the abundance of weakly acidic weathered igneous rocks around Nairobi, Kenya, in order to fully improve the adhesion performance of asphalt and acidic igneous rocks, this paper studies the effects of different anti-stripping agents separately and combined on the adhesion performance of asphalt aggregates. The results show that the anti-stripping agent can improve the anti-stripping property of the medium weathered igneous rock aggregate and asphalt, and the effect is better when the anti-stripping agent is combined.

NATURAL CRUSHED ROCK AS AGGREGATE FOR ULTRA HIGH STRENGTH CEMENT CONCRETES

Because of strong competition and new trends of concrete construction, cement industry isstarting to offer cement of high class in world markets (62.5; 72.5; 82.5) with whom production ofultra hard concretes of 100 MPa up to 250 MPa of withstanding is possible. To achieve suchwithstanding, not only cement of high class are needed but also rock aggregates of at least 30% higherrigidity than the required rigidity of concrete. Technological solutions for this kind of concrete will behighly demanded by the cement industry, civil engineering industry and industry for the exploitation ofraw mineral materials. Production of such crushed aggregates will find its use in the production of ultrahigh rigidity concretes and will open new surroundings.This paper offers the overview of tests in laboratories conducted on samples of aggregates made ofgabbro rock under Nero Zimbabwe’s name, as an initial phase of research. In later phases itcovers a larger number of above mentioned samples from various excavation sites, with a specialaccent on these kinds of sites in former Yugoslavia. It is expected that these premises may havereserves of rock aggregate resistant to pressures of 150 MPa to 330 MPa which would openpossibilities of constructing ultra high rigidity concretes.In addition to analyzing the required production of ultra high strength concrete, the authors consciouslypoint out the problem of interpreting the mechanical characteristics of the material. The technicalprofession does not consider the physical state of the investigated materials, where the compressivestrength of concrete is in the form of relative strength. From the aspect of legal sciences, the concept ofrelative at the construction of large and small objects can cause legal consequences for the constructorand its profession.

Assessment of Rock Aggregate for Construction Using Comminution Theory

In this research, grinding energy of selected rock samples collected from South West Nigeria was determined using comminution theory in order to evaluate suitability of rock for aggregate production. Bond Work Index (BWi), Aggregate Impact Value (AIV) and Aggregate Crushing Value (ACV) of samples was characterized and correlated. The work index of the charnockitic rock, granite gneiss, porphyritic granite –labelled PG1 and porphyritic granite –labelled PG2 of samples was found to be 17.12 kWh/t, 13.72 kWh/t, 13.64 kWh/t and 12.76 kWh/t respectively. The ACV of the charnockitic rock, granite gneiss, porphyritic granite (PG1) and porphyritic granite (PG2) was determined to be 26.2 %, 27.3 %, 27.6 % and 27.8 % respectively; while the AIV of the samples, in same order, was 11.2 %, 13.2 %, 19.1 % and 18.4 % respectively. Following high correlation coefficient of 0.98% between BWi and ACV, hardness of rock materials are classified as ‘very difficult’, ‘difficult’, ‘medium’, ‘easy’ and ‘very easy’ for grinding energies in the range of >18 kWh/t, 14-18 kWh/t, 10-14 kWh/t, 7-10 kWh/t and 0-7 kWh/t respectively. Based on the classification, rock materials with grinding energy >10 kWh/t could be suitable for aggregate production and usable for civil construction purposes.Keywords- Aggregate, Aggregate impact value, Aggregate crushing value, Comminution, Grinding energy.