Aggregate Mineralogy Research Articles

A review of mechanical properties and carbonation behavior evolution of lime mortar for architectural heritages restoration

Using lime mortar to connect, protect and decorate buildings was a very common technique in ancient times. Understanding the mechanical properties and carbonation mechanism of lime mortar is the basis for successful restoration and protection of architectural heritage. The compatibility and durability of lime mortar and architectural heritage promote the study of related mechanisms, so that it can adapt to the current reality. In this paper, the factors affecting the mechanical properties of lime mortar are summarized, and the carbonization principle of lime mortar is analyzed. The effects of water-binder ratio, aggregate mineralogy and particle size, inorganic additives and organic additives on the mechanical properties of lime mortar were elaborated in detail, especially the action behavior of organic additives in the carbonation process of lime mortar. Suggestions for enhancing the mechanical properties of lime mortar are put forward, which provides a theoretical basis for improving the compatibility and durability of materials in the restoration of ancient buildings.

Multiscale investigation on bitumen-aggregate interfacial debonding using molecular dynamics and finite element method

Adhesive failure between bitumen and aggregates is the primary cause of cracking in asphalt mixtures and pavement moisture damage. The resulting pavement distress poses a significant challenge to the service durability of the road infrastructure. Previous studies have validated that aggregate mineralogy has a significant influence on the adhesion properties between bitumen and aggregates; however, there is still a lack of a mechanistic understanding of the influence of the mineral constitution and distribution on the interfacial debonding behavior. This study aims to fill this knowledge gap by proposing a multiscale approach based on molecular dynamics (MD) simulations and the finite element method (FEM). First, the MD method was employed to extract the traction-separation curve of the interface between bitumen and minerals at a molecular scale. The obtained traction-separation relationship was then utilized as the input parameter for the zero-thickness cohesive element in the microscale bitumen-aggregate finite element model. The combined simulation results indicate that quartz with bitumen has the best cracking resistance at the molecular scale, followed by albite, mica, pyroxene, and anorthite. Among the three selected aggregates, the greywacke aggregate exhibited the best cracking resistance at the microscale level. Moreover, the distribution microstructure of the minerals was found to affect the cracking path of the bitumen-aggregate interface, and the bitumen-mica interface elements at the junction area with quartz have a late debonding. The proposed research method spearheads the prediction of multiscale bitumen-aggregate interfacial behavior by considering the aggregate mineralogical heterogeneity.

Microstructure, tensile strength and shear strength of aggregate-mortar interface: Effect of aggregate mineralogy

This work aims to study the mechanical properties of the interfacial transition zone (ITZ) through both experimental tests and microstructural observations. The study considers a mortar with water-cement ratio of 0.58 and four types of aggregates: sandstone, granite, and two different types of limestone with varying water absorption coefficients. Chemical compositions, physical characteristics, and surface micromorphology of the four aggregates were evaluated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and water absorption measurements as well as SEM observations. Experimental setups were developed to investigate the bonding behavior of the aggregate-mortar interface. The bonding strength between granite and mortar through direct tensile test varied from 51% to 69% of tensile strength of mortar from young age to mature, while 61% to 74% for sandstone, 48% to greater than 90% and 81% to greater than 102% averagely for black and white limestone respectively. The fact of failure in the bulk mortar indicates ITZ adhesion for limestones may equal or exceed the mortar tensile strength generally from 28-day age. This conclusion is consistent with the results obtained by slant shear test. The significant difference of adhesion behavior of ITZ between two limestones due to their water absorption capability. High-water absorption turns out to be beneficial in forming a strong chemical bond at early age, however, the mineralogy remains the pivot under same surface condition. This chemical bond is evidenced by the failure pattern and morphology of the aggregate surface after failure and the presence of a dense accumulation of portlandite and C-S-H under SEM.

The effect of paste composition, aggregate mineralogy and temperature on the pore solution composition and the extent of ASR expansion

The reaction kinetics of the alkali silica reaction depends on the composition of the pore solution. The evolution of the pore solution composition in different cement pastes and concretes was studied. Pastes containing silica fume or metakaolin had the lowest amount of alkalis in the pore solution. In addition, metakaolin increased the aluminium concentrations. The lowest expansion was measured for the concretes made of blended cement pastes with low alkali and hydroxide content in their pore solution, for the duration of the present study, no additional aluminium effect was observed due to the already low pH. Addition of 400 mM of Li slowed down expansion rate of concrete prisms at 40 and 60 °C, however, similar expansion was observed for samples with and without Li at 60 °C after 1 year. Temperature, alkali concentration and pH of pore solution all have a major effect on ASR expansion.

Experimental investigation of optimum adhesion properties for anionic emulsions in road maintenance applications

Anionic emulsions are widely used in North America for road maintenance applications but are less popular in Europe. Due to their distinctive characteristics, the use of anionic emulsions is advantageous when local aggregate is excessively dusty and the cost to wash them to meet requirements would be too expensive. However, anionic emulsions’ compatibility, in terms of adhesion, with certain types of aggregate is reported to be limited. This paper presents the results of an experimental study that was conducted firstly to investigate the effect of aggregate mineralogy on the degree of adhesion (i.e. the bond) between the aggregate and the bitumen using anionic and cationic bitumen emulsions, and secondly to evaluate the potential development and use of new adhesion agents/anti-strips for anionic rapid-set emulsions used in chip seal applications. For this purpose, the degree of adhesion that was achieved between the emulsions used and a range of selected aggregates was measured by means of a series of internationally recognised laboratory adhesion tests.The experimental laboratory work confirmed that the degree of adhesion between the aggregate and emulsion is governed to a large extent by aggregate mineralogical composition and, in particular, its associated electrostatic interaction with a given emulsion. The results obtained indicated that a higher degree of adhesion was achieved when an aggregate was combined with an emulsion possessing the opposite surface charge. Further laboratory test results suggest that the addition of amine-based adhesion agents to an anionic emulsion can significantly improve its degree of adhesion with aggregates possessing an electro-negative surface charge.

Effects of Aggregate Shape and Mineralogy on Relationships between Concrete Mechanical Properties

Effects of Aggregate Shape and Mineralogy on Relationships between Concrete Mechanical Properties

Effect of coarse aggregate mineralogy on micro-texture deterioration and polished stone value

The objective of the study presented in the paper is to identify the mineralogical parameters that influence both micro-texture deterioration and Polished Stone Value (PSV), which are the two most important properties of the aggregates that control the pavement skid resistance. The study was carried out on fourteen sources of aggregates which belong to either igneous or metamorphic rock category, the two most commonly used aggregate categories for surface course mixtures in India. PSV of aggregates was determined as per BS EN 1097-8: 2009. To investigate the progressive extent of polishing, the British Pendulum Number (BPN) of the aggregate was determined after every hour of polishing. Simultaneously, the mineralogical parameters were also obtained based on the microscopic observations of the thin sections of the aggregates. From accelerated polishing tests, it was observed that igneous aggregates, especially granites, were found to have relatively high PSV and good polishing resistance. Nevertheless, granite aggregates with altered minerals witnessed poor polishing resistance. Correlation analysis on the combined data for igneous and metamorphic aggregates suggested that the mineralogical parameters such as Relative Hardness (RHD) of aggregates, Differential Hardness (DH) between major minerals within the aggregate, and degree of alteration (DA) influence micro-texture deterioration rate (BPN3-BPN6). PSV showed a good correlation with RHD and DH. It was also noted that altered granite aggregates of igneous type significantly influenced the correlation. In general, it was observed that fundamental mineralogical parameters can better predict BPN3-BPN6 than PSV.

New Chemical Reactivity Index to Assess Alkali–Silica Reactivity

Despite the awareness of the alkali–silica reaction (ASR) since 1940, the need for an efficient and reliable method of evaluating the potential reactivity of aggregates for use in concrete still exists. Current standards to assess the ASR susceptibility of aggregates have limitations due to inherent problems with accelerated testing conditions. This paper introduces a novel chemical reactivity index (RI) to evaluate the alkali–silica reactivity of coarse aggregates or concrete mixtures by exposing samples to a simulated pore solution with composition mimicking that expected in the concrete. Based on the mix design to be evaluated, aggregate samples are exposed to an alkaline solution of appropriate concentration and fixed amounts of CaO. The newly proposed alkali–silica RI is calculated based on the concentrations of silicon, aluminum, and calcium in solution after 21 days of exposure at 55°C. This RI, sensitive to alkali concentration and aggregate mineralogy, exhibited strong agreement with physical expansion.

Multiscale understanding of interfacial behavior between bitumen and aggregate: From the aggregate mineralogical genome aspect

The interfacial behavior between bitumen and aggregate is not well understood so far since it is sensitive to various factors including chemistry of the components, morphology of the interface, and the environmental and loading conditions. Moreover, the mechanisms of action for different factors occur at distinct time and length scales. The multi-factor and multi-scale natures bring great challenge to the interfacial behavior between bitumen and aggregate. This study aims to exploit a deep understanding of the interfacial behavior from the perspective of aggregate mineralogy at the molecular scale and relate this fundamental understanding to affinity between bitumen and aggregate. For this, the affinity between bitumen and six kinds of aggregates were evaluated by the rolling bottle test, and adhesion mechanisms between bitumen and component minerals were investigated through molecular dynamics simulations. The rolling bottle test results show that the diabase has the best moisture damage resistance, followed by the greywacke I, basalt and greywacke II. The two granite aggregates show the worst moisture damage resistance. The molecular dynamics simulation indicates the existence of competitive adsorption between bitumen and water molecules at the mineral surface, and the penetration capacity of bitumen molecule is greatly affected by the mineral property. Aggregates with higher content of nepheline, chlorite, pyroxene and olivine minerals are more likely exhibit better moisture damage resistance while aggregates with higher content of quartz, plagioclase and calcite minerals do the opposite. The findings from this research provide insights into the underlying mechanism of aggregate mineralogy influence on affinity between bitumen and aggregate.

Predicting Long-Term Coefficient of Thermal Expansion of Paving Concrete

The coefficient of thermal expansion (CTE) of concrete is an important parameter that affects the design and performance analysis of concrete pavements. Higher CTE value results in increased curling and related stresses. A 28-day CTE value is used for designing rigid pavements. Though previous studies have revealed that coarse aggregate mineralogy has substantial effects on the CTE value of paving concrete, it is not known yet how CTE value changes with the age of concrete in the long-term. In this study, seven concrete mixes with different coarse aggregate mineralogy are tested in the laboratory and data is analyzed to examine CTE. Results show that limestone has the lowest CTE values compared with other coarse aggregates. Concrete CTE increases from 6.4% to 12.6% as it ages. This increase in CTE may result in increased thermal distresses as concrete pavement ages. Therefore, a single value of 28-day CTE should not be used in the design of concrete pavements. In this study, a prediction model is developed to determine aged CTE incorporating mixture volumetrics and concrete strength properties. The same can be incorporated in Pavement Mechanistic Empirical (ME) Design software to better predict the rigid pavement performance.

Impact of aggregate mineralogy and exposure solution on alkali-silica reaction product composition and structure within accelerated test conditions

Electron microscopy, chemical X-ray microanalysis, and Raman microscopy was used with expansion measurements of mortar bars in a systematic fashion to determine the impact of aggregate composition and exposure variations on alkali-silica reaction (ASR) products’ chemistry and structure. The results show that aggregate mineralogy plays a large role in the composition and structure of ASR products as does the local environment in which ASR products form. Additionally, solution exposure composition, a factor relevant to relating laboratory measurements to field performance, has a significant impact on ASR product chemistry but limited impact on structure, or at least on coordination of SiO2 in ASR products.

Moisture susceptibility of hydrated lime modified mastics using adhesion test methods and surface free energy techniques

ABSTRACT Moisture damage is one of the major factors that has been reported to affect the performance of asphalt pavements which depends mainly on the bond strength between bitumen, aggregates and mineral filler. In the presence of moisture, this bond weakens and results in premature pavement failure. One of the many ways of mitigating moisture damage effects is the use of anti-stripping agents. Hydrated lime has been found to be one of the most efficient anti-stripping agents among the common additives used with asphalt mixtures. This study attempts to quantify the bond strength of hydrated lime modified mastics with different aggregates (granite and limestone) under moisture conditions using a combination of surface free energy techniques and conventional adhesion test methods. From the surface free energy technique, the moisture susceptibility was studied in the form of dry work of adhesion, work of debonding and various energy parameters. Two conventional techniques, the PATTI test and the rolling bottle test were used to assess bond strength under wet conditions. The results of all three techniques lead to the same conclusion that hydrated lime is an active filler that improves moisture damage resistance compared to the other natural fillers but that the improvement is highly dependent on aggregate mineralogy.

Influence of Environmental Conditions on the Performance of Bituminous Mixtures

Abstract Aging and moisture damage are considered as major environmental factors which affect the performance of bituminous mixtures. This study investigated the effect of aging and moisture invasion on the performance of bituminous mixtures in terms of tensile strength and rutting resistance. Two different types of aggregates sources and one unmodified bituminous binder with and without warm additive were used. Bituminous mixtures were subjected to two levels of aging conditions (short-term and long-term aged) and two levels of moisture conditions (1 and 3 freeze-thaw cycles). A total of 24 different combinations were investigated for tensile strength and permanent deformation characteristics. Mineralogical investigations characterized the crushed stone as calcareous and bank run as siliceous aggregates. Results from this study demonstrate that levels of aging had a significant impact on the tensile strength of bituminous mixtures with warm mix additive as compared to conventional bituminous mixtures. Fracture work density, a surrogate cracking parameter was able to adequately capture the influence of aggregate mineralogy on the moisture susceptibility of long term aged mixtures. In addition, moisture conditioning was found to influence fracture work density of mixtures more than aging. Further, the rutting resistance of mixtures was determined in terms of flow numbers obtained using Francken model. In general, the rutting resistance of conventional mixtures was relatively higher than a mixture with warm mix additive. As expected, the flow number of conventional mixtures increased with aging and further reduced with moisture conditioning. Interestingly, the flow numbers of bituminous mixtures with warm mix additive was not negatively impacted by moisture at short term aged conditions. However, flow number of both mixtures after long term aging exhibited a similar trend. Additionally, statistical analysis showed that an increase in freeze-thaw cycles from one to three did not significantly impact the tensile characteristics of the mixtures.

Effect of Aggregate Mineralogy and Concrete Microstructure on Thermal Expansion and Strength Properties of Concrete

Aggregate type and mineralogy are critical factors that influence the engineering properties of concrete. Temperature variations result in internal volume changes could potentially cause a network of micro-cracks leading to a reduction in the concrete’s compressive strength. The study specifically studied the effect of the type and mineralogy of fine and coarse aggregates in the normal strength concrete properties. As performance measures, the coefficient of thermal expansion (CTE) and compressive strength were tested with concrete specimens containing different types of fine aggregates (manufactured and natural sands) and coarse aggregates (dolomite and granite). Petrographic examinations were then performed to determine the mineralogical characteristics of the aggregate and to examine the aggregate and concrete microstructure. The test results indicate the concrete CTE increases with the silicon (Si) volume content in the aggregate. For the concrete specimens with higher CTE, the micro-crack density in the interfacial transition zone (ITZ) tended to be higher. The width of ITZ in one of the concrete specimens with a high CTE displayed the widest core ITZ (approx. 11 µm) while the concrete specimens with a low CTE showed the narrowest core ITZ (approx. 3.5 µm). This was attributed to early-age thermal cracking. Specimens with higher CTE are more susceptible to thermal stress.

Influence of cement alkalis on mortar expansion of ASTM C 1260

The main objective of this study was to evaluate the influence of three dosages of cement alkalis, such as 0·42, 0·84 and 1·26% Na2Oeq, on the alkali–silica reactivity-induced expansion of mortar bars prepared with 14 aggregate groups for 1·0, 0·5 and 0·25 N sodium hydroxide solutions at test durations of 14, 28, 56 and 98 d. For each alkali solution, the percentage contribution of cement alkali, test duration and their interaction to mortar expansion was also evaluated. The study revealed that, regardless of aggregate mineralogy, the influence of cement alkalis on mortar expansion depended mainly on the alkali solution concentration and test duration. The effect was more severe for the reduced concentration of alkali solution and early test duration, whereas the influence was minor for higher concentrations of alkali solution and extended test durations. Elevating cement alkalis resulted in a greater increase in the expansion of reactive aggregates for 0·25 N sodium hydroxide as compared to that of innocuous aggregates.

AN OVERVIEW OF MOISTURE DAMAGE PERFORMANCE TESTS ON ASPHALT MIXTURES

This paper presents a review of moisture damage performance tests on asphalt mixtures. The moisture damage remains to be a detriment to the durability of the Hot Mix Asphalt (HMA) pavement. Moisture damage can be defined in forms of adhesive failure between bitumen and aggregates and cohesive failure within bitumen. Aggregate mineralogy, bitumen characteristics and anti-stripping additive dominantly influence the performance of asphalt mixtures towards moisture damage alongside construction methods, climate and traffic loading. Various laboratory test methods have been developed to quantify the moisture damage performance of asphalt mixtures by resembles the action in the field, including qualitative test such as Boiling Water Test (ASTM D3625) and quantitative tests such as Modified Lottman Test (AASHTO T283). Both of these tests consist of two phases, which are conditioning and evaluation phase. This paper will review the effectiveness of the selected available tests based on various asphalt mixtures materials. Generally, this study indicates that asphalt mixtures consisted of limestone aggregates, modified bitumen and addition of anti-stripping additives will provide more resistant towards moisture damage.

Confirming a pyrolitic lower mantle using self‐consistent pressure scales and new constraints on CaSiO3 perovskite

AbstractIn this study, we have examined the lower mantle composition and mineralogy by modeling the density (ρ), bulk sound velocity (VΦ), and dlnρ/dlnVΦ profiles of candidate lower mantle minerals using literature and new experimental equation of state (EoS) results. For CaSiO3 perovskite, complimentary synchrotron X‐ray diffraction measurements in a laser‐heated diamond anvil cell were conducted up to 156 GPa between 1200 K and 2600 K to provide more reliable constraints on the thermal EoS parameters. These new experimental results as well as literature P‐V‐T data sets are systematically analyzed using an internally self‐consistent pressure scale. We have modeled ρ, VΦ, and dlnρ/dlnVΦ profiles of the lower mantle with representative pyrolitic and chondritic compositional models in which the effect of Fe spin transition in ferropericlase is also taken into account. Our modeling results show that a pyrolitic lower mantle with an aggregate mineralogy of 75 vol % bridgmanite, 17 vol % ferropericlase, and 8 vol % CaSiO3 perovskite produces ρ and VΦ profiles in better agreement with preliminary reference Earth model than a lower mantle with a chondritic composition. The modeled ρ, VΦ, and dlnρ/dlnVΦ are mainly affected by the relative ratio of bridgmanite and ferropericlase but are not sensitive to the variation of the CaSiO3 perovskite content. In addition, the spin crossover of Fe in ferropericlase can greatly raise the value of dlnρ/dlnVΦ in the middle lower mantle, which is useful in detecting the presence of ferropericlase in the region. Based on these new mineral physical constraints and radial seismic structure, our study suggests the lower mantle is pyrolitic, which is chemically indistinguishable from the upper mantle.

CAN THE ACCELERATED PRISM TEST EVALUATE ALKALI-SILICA REACTIVITY?

The purpose of this study was to evaluate the alkali-silica reactivity of twelve aggregates based on the ASR-induced expansions of ASTM C 1260 and modified ASTM C 1293. The mortar bars and concrete specimens were prepared and fully submerged in the 1.0N NaOH at the temperature of 80°C. The ASR-induced expansions of the test specimens were recorded at various immersion ages. The expansion limits of alkali-cured prisms were proposed at the test durations of 4 and 8 weeks. Finally, the trial aggregates were classified based on the aggregate mineralogy and the expansion limits of mortar bars at 14 and 28 days, and they were compared with the proposed expansion limit of concrete prisms at the ages of 4 and 8 weeks. It was acknowledged that the 4-week failure limit of concrete prisms under the 1.0N resulted in some innocuous aggregates to be rated as reactive. However, the ASR-classifications of the trial aggregates showed a perfect correlation based on the results obtained from the extended failure limits of mortar bars and concrete prisms, and those from the mineralogy of aggregates.

KINETIC MODEL TO PREDICT ULTIMATE MORTAR EXPANSION

This study reports the prediction of ultimate mortar expansion (UME) due to alkali-silica reactivity. The investigated sixteen aggregate groups with a wide range of geology and mortar expansion that were utilized in this study were obtained from two existing experimental studies. The expansions over the 28-day testing period were fitted with the ASR decay model to predict the UME and time required to reach 50%, 75%, 90% and 95% of UME. The study showed that the ultimate mortar expansion varied with aggregate mineralogy. Finally, aggregates susceptible to alkali-silica reactivity were determined based on the proposed limit of ultimate mortar expansion, and they were compared with the results obtained by the aggregate geology and expansion limits at test durations of 14 and 28 days.

Forensic investigation of the cause(s) of slippery ultra-thin bonded wearing course of an asphalt pavement: influence of aggregate mineralogical compositions

The cause(s) of slippery ultra-thin bonded wearing course (UTBWC) of an asphalt pavement was investigated. Petrographic analysis showed that the aggregate used in the UTBWC is mainly limestone with an average acid-insoluble residue of 5.1%. Coefficient of friction tests were performed both on a comparative UTBWC from Virginia with a different aggregate mineralogy VA-UTBWC and on slabs extracted from the slippery UTBWC pavement overlay. The tests clearly showed that the slippery UTBWC overlay sharply declined throughout the polishing process, consistent with the aggregate mineralogical composition and its low amount of acid-insoluble residue. In contrast, the comparative VA-UTBWC mix showed a gradual increase and then decrease in friction with continued polishing. This investigation clearly showed that the cause of the slippery asphalt pavement problem of the road mainly attributed to limestone aggregate polishing.