Mortar Aggregate Research Articles

Basic creep and fracture response of fine recycled aggregate concrete

We investigate the basic creep and fracture response of fine recycled aggregate concrete using nanoscale mechanical characterization modules integrated with nonlinear micromechanical modeling and machine learning methods. Fine recycled concrete aggregate mortar exhibits a larger volume fraction of micropores and low-density calcium silicate hydrates compared to natural sand mortar. In return, natural sand mortar exhibits a larger volume fraction of hard aggregates. The macroscopic logarithmic creep modulus for fine recycled concrete aggregate mortar is five times lower than that of natural sand mortar. Finally, the fracture toughness of fine recycled aggregate concrete is 8% lower than that of plain concrete.

Expansive behavior of an alkali-carbonate reactive dolostone from Argentina: Proposal of an osmotic theory-based model to explain the expansion caused by the alkali attack

The expansion mechanism of dolomitic rocks in alkaline environments is complex and a current topic of debate, since two different chemical reactions can coexist: one linked with silica attack (alkali-silica reaction, ASR) and the other with dolomite attack (alkali-carbonate reaction, ACR). In previous works, a potentially reactive, fine-grained argillaceous dolomitic rock was identified in Argentina, with similar expansive characteristics to the typical American reactive carbonates. When this rock is used as aggregate in mortars or concretes, the dolomite experiences a clearly expansive dedolomitization reaction, which cannot be controlled by the classical techniques that allow the inhibition of ASR: supplementary cementitious materials (SCMs) (fly ash, natural pozzolan, silica fume, etc.) or Li-based admixtures. Since none of the classical theories proposed by the literature adequately describe the expansive behavior of this rock, an expansion mechanism based on the osmotic phenomenon is proposed in the present work. This mechanism describes the behavior of the Argentine dolostone more appropriately and allows explaining the effect of the main factors involved in the concrete expansion (pH of the pore solution, nature of the alkali cation associated with the OH−, role of water in the expansion, temperature, aggregate particle size, effect of the SCMs, etc.). The basis of the osmotic model is presented, and its advantages are discussed compared with the classical ACR mechanisms proposed by the literature.

Strength, Drying Shrinkage, and Carbonation Characteristic of Amorphous Metallic Fiber-Reinforced Mortar with Artificial Lightweight Aggregate.

This paper investigates the strength, drying shrinkage, and carbonation characteristic of amorphous metallic fiber-reinforced mortar with natural and artificial lightweight aggregates. The use of artificial lightweight aggregates has the advantage of reducing the unit weight of the mortar or concrete, but there is a concern that mechanical properties of concrete such as compressive strength and tensile strength may deteriorate due to the porous properties of lightweight aggregates. In order to improve the mechanical properties of lightweight aggregate mortar, we added 0, 10, 20, and 30 kg/m3 of amorphous metallic fibers to the samples with lightweight aggregate; the same amount of fiber was applied to the samples with natural aggregate for comparison. According to this investigation, the flow of mortar decreased as the amount of amorphous metallic fiber increased, regardless of the aggregate type. The compressive strength of lightweight aggregate mortar with 10 kg/m3 amorphous metallic fiber was similar to that of the LAF0 sample without amorphous metallic fiber after 14 days. In addition, the flexural strength of the samples increased as the amount of amorphous metallic fiber increased. The highest 28-d flexural strength was obtained as approximately 9.28 MPa in the LAF3 sample, which contained 30 kg/m3 amorphous metallic fiber. The drying shrinkage of the samples with amorphous metallic fiber was smaller than that of the sample without amorphous metallic fiber.

Hydration and Microstructure of Steel Slag as Cementitious Material and Fine Aggregate in Mortar.

Due to the low hydration activity and poor volume stability, extensive steel slag utilization is restricted. In this paper, the hydration process and microstructure of alkali-activated materials with steel slag as a cementitious material and fine aggregate were studied. The phase composition and micro-morphology of hydration products were measured using XRD, NMR and SEM. The response relationship between microstructure and mechanical properties during hydration was revealed. The results show that the main hydration products of the alkali-activated steel slag powder-granulated blast furnace slag powder cementitious system are Ca(OH)2 and calcium aluminosilicate hydrate (C-A-S-H) gel. With the progress of hydration, the amount of calcium silicate hydrate (C-S-H) gel and the average molecular chain length increase, Al[4]/Si decreases, while C/S increases first and then decreases, and the structure of cement paste becomes much more compact. The interface between steel slag sand and cement paste is denser than that of river sand, since the hydration occurs on the surface of steel slag sand, which leads to the formation of C-A-S-H gel and Ca(OH)2. As a result, the compressive strength of concrete prepared by steel slag sand is higher than that of river sand with the same mix proportion.

Nanostructure of calcium-silicate-hydrates in fine recycled aggregate concrete

Our research objective is to foster a multiscale understanding of fine recycled aggregate concrete using a bottom-up approach. We investigate the influence of fine recycled concrete aggregates on the structure of calcium-silicate-hydrates. To this end, we introduce a new thought model for fine recycled aggregate concrete with four levels of structural hierarchy: beam, mortar, binder, and C–S–H gel levels. We characterize the behavior of fine recycled aggregate concrete and natural sand concrete using analytical methods such as X-ray diffraction, and scanning electron microscopy, along with depth-based mechanical testing methods such as micro-indentation and nano-indentation. Micromechanical modeling integrated with statistical deconvolution methods is applied to quantify the phase distribution of natural sand mortar and fine recycled concrete aggregate mortar. We observe that fine recycled aggregate concrete exhibits a higher volume fraction of calcium silicate hydrates. Furthermore, the presence of fine recycled concrete aggregates leads to nanostructural changes at the C–S–H gel level. Fine recycled aggregate concrete exhibits a higher volume fraction of loosely-packed low-density calcium silicate hydrates compared to natural sand concrete. Calcium silicate hydrates in fine recycled aggregate concrete exhibit a higher C–S–H gel porosity. Finally, the C–S–H gel porosity in fine recycled aggregate concrete accounts for 56.2% of the total porosity. These results suggest that to improve the mechanical and transport properties of fine recycled aggregate concrete, it is essential to reduce the C–S–H gel porosity of calcium silicate hydrates and increase the fraction of optimally-packed high-density calcium silicate hydrates.

Recycling of waste glass in dry-mixed concrete blocks: Evaluation of alkali-silica reaction (ASR) by accelerated laboratory tests and long-term field monitoring

Alkali-silica reaction (ASR) restricts the practical applications of recycled waste glass aggregates in concrete. Recent investigations according to ASTM C1260 (laboratory test) found that ASR expansion of glass aggregates in dry-mixed mortars could be minimized as compared with the excessive ASR expansion in wet-mixed mortars. This study aimed to validate the benefit of the dry-mixed method by a long-term (15 years) field monitoring, as no study had been reported on the long-term ASR behavior of glass based dry-mixed mortars before. The results showed that the development process of the ASR gel of the glass aggregates in the dry-mixed mortars tested by the laboratory tests (ASTM C1260 and ASTM C227) was consistent with the long-term field monitoring results. According to ASTM C227 (laboratory test), after six months of the ASR test, the ASR gel was firstly identified only on the exterior surface of the glass aggregates in the macro pores of the dry-mixed mortars (exterior-glass ASR gel), which did not cause expansion. Later, the ASR gel was observed within the interior pre-existing cracks of the glass aggregates (interior-glass ASR gel). For the long-term tested blocks collected from the field, only exterior-glass ASR gel was detected in the 15 years old blocks because of the much slower ASR rate in the field. No ASR induced crack was observed. The results of the study also showed that the additional use of glass powder as a supplementary cementitious material was effective to control the formation of the deleterious interior-glass ASR gel in the dry-mixed mortars, which could further increase the usage of waste glass in concrete blocks.

A study on rheological properties of rubber fiber dosed self-compacting mortar

The improper disposal of waste rubber tires leads to severe environmental and health issues, which can be mitigated through the use of waste tire rubber particles as construction material. In the present study, use of fiber shaped rubber particles has been explored as fine aggregates (up to 25%) in self-compacting mortar (SCM). Fresh state properties of SCM mixes have been studied using conventional and rheological tests. Conventional tests have been used to evaluate air content, fresh density, flow time (using mini V-funnel), and flow spread (using mini-slump). Rheological tests have been used to observe the flow curves (shear stress and viscosity curves), dynamic yield stress, plastic viscosity, shear thinning behaviour and thixotropic behaviour. Particle interaction in fresh state has also been observed using optical microscopy. Results indicate that air content and flow time increase with rubber fiber incorporation whereas the fresh density and flow spread decrease with rubber fiber incorporation in SCM mixes. Addition of rubber fiber exhibited a loss of flow characteristics (increase in dynamic yield stress and plastic viscosity) in SCM mixes. Shear-thinning behaviour was observed for all mortar mixes with the highest intensity of shear-thinning in 15% rubber fiber mortar. Thixotropy was observed to increase with rubber content. As per the acceptance limits defined for conventional tests, up to 15% rubber fiber can be used for the preparation of SCM in the adopted mixes.

Natural hydraulic lime mortars - The effect of ceramic residues on physical and mechanical behaviour

In the past, it was common the use of ceramic residues as a pozzolan and/or aggregate in air lime mortars and concrete. Nowadays, incorporating ceramic residues in mortars is one of the ways to increase sustainability of the construction sector and introduce some benefits in the properties of those mortars.Ceramic residues were collected from several ceramic industries, namely from bricks, roof tiles and pots production, milled in laboratory and incorporated in natural hydraulic lime (NHL) mortars. Two distinct groups of mortars were prepared, with two different proportions, and samples were produced. A group with a volumetric proportion of one part of NHL and three parts of aggregate (1:3) and three different percentages of replacement of the aggregate by each of the residues (0, 20 and 40% in volume) and a second group with a volumetric proportion of one part of NHL and four parts of aggregate (1:4) and percentages of replacement of 0 and 30% were prepared. Their behaviour was analysed by determining its properties after 28 days of curing.The incorporation of ceramic residues in the NHL mortars led to an increase in open porosity, capillarity water absorption and water vapour permeability but also an increase in dynamic elasticity modulus and mechanical strengths. This increase was more significant for higher replacement percentages. The behaviour of these mortars seems appropriate for new construction renders and plasters but caution must be taken concerning moisture migration, namely when used in rehabilitation.

A smoothed particle hydrodynamics study on effect of coarse aggregate on self-compacting concrete flows

Coarse aggregates increase inhomogeneity and alter rheological properties of self-compacting concrete. In this work, the effect of coarse aggregates on self-compacting concrete is studied by considering its pipe flow. Self-compacting concrete is modelled as suspension of coarse aggregates in cement mortar and a two-phase Smoothed Particle Hydrodynamics (SPH) model is employed. Cement mortar, a yield-stress fluid, is modelled by fluid SPH particles, while each coarse aggregate is represented by a group of solid SPH particles, which moves as a rigid body. Simulation results show that, at the same volume fractions, the flow rate is higher for larger coarse aggregates, that is up to 24% in the investigated cases. Both effective yield stress and effective plastic viscosity of the concretes increase with the coarse aggregate content. Effective yield stress is smaller for bigger coarse aggregates. The reduction in effective yield stress is a consequence of bigger averaged gap between larger coarse aggregates through which the cement mortar flows.

Study on the use of lightweight expanded perlite and vermiculite aggregates in blended cement mortars

This paper presents an experimental investigation on lightweight aggregate mortars containing high volume cement replacement materials. For this purpose, expanded perlite (EP) and expanded vermiculite (EV) are used as the lightweight aggregate (at sand replacements of 50% and 100%), while ground granulated blast furnace slag (GGBS) (35% and 70% replacement level) and fly ash (25% and 50% replacement level) are adopted as the supplementary cementitious materials (SCMs). The results showed that EP is beneficial for improving the flow of fresh mortar, and soft mortar (flow diameter > 200 mm) can be produced by using EP in SCM-cement blends. Both EP and EV can be utilised to produce lightweight mortar in the density range of 1400–1700 kg/m3 and 900–1100 kg/m3 at 50% and 100% sand replacements, respectively. Although the lightweight aggregates resulted in compressive strength decrease, the developed lightweight mortar using 50% EP (with or without SCMs) can be classified as type N mortar (compressive strength exceeding 5.17 MPa) while those prepared with 100% EP as well as 50% EV can be categorised as type O mortar. Response surface methodology carried out in this study also demonstrated that the mathematical equations can suitably estimate the studied performances of the lightweight mortars.

Physical Properties and Microstructure of Concrete with Waste Basalt Powder Addition.

The natural aggregates are one of the main components in the production of concrete. Although deposits of natural aggregates lie on the earth’s surface or at low depths and belong to common deposits, the shortage of aggregate, especially natural sand, is presently observed in many countries. In such a situation, one is looking for other materials that can be used as a substitute for natural aggregates in mortars and concrete production. This paper presents the results of an experimental investigation carried out to evaluate the potential usage of waste basalt powder in concrete production. For this purpose, the waste basalt powder, which is a by-product of the production of mineral–asphalt mixtures, was substituted with 10%, 20%, and 30% sand replacement. In the experimental program, the workability, compressive strength, water transport properties, and microstructural performances were evaluated. The results showed that the production of concretes that feature a strong internal structure with decreased water transport behavior is possible with waste basalt usage. Furthermore, when waste basalt powder is used as a partial sand replacement, the compressive strength of concretes can be increased up to 25%. According to the microstructural analyses, the presence of basalt powder in concrete mixes is beneficial for cement hydration products, and basalt powder substituted concretes have lower porosity within the interfacial transition zone.

Utilization of garnet residue in radiation shielding cement mortar

This experimental investigation was carried out to evaluate the potential of garnet residue, a by-product from the abrasive industry, as an aggregate in cement mortar through the physical, mechanical, microstructure, leaching and radiological properties. The findings revealed that the sand replacement by garnet residue enhanced the physical and mechanical properties. In radiological experiments, the cement mortar incorporating garnet residue at 100% by weight improved both gamma-ray and neutron shielding properties at 34% and 26%, respectively, better than the control sample. Thus, based on these results, it is concluded that the percentage of garnet residue can fully replace sand in radiation shielding cement mortar.

ASR expansion of alkali-activated cement glass aggregate mortars

Previous studies showed using calcium aluminate cement (CAC) can effectively mitigate the alkali-silica reaction (ASR) expansion of alkali-activated cement (AAC) mortars incorporating glass cullet (GC) as fine aggregates but the mechanism was not clear. This study presents a systematic study on exploring the underlying mechanism to fill in the knowledge gap and to ascertain the safe use of GC in AAC to maximize the possibility of recycling of waste glass in construction materials. The results showed that the ASR expansion of alkali-activated glass mortars was more than 1000 με after 1 day of alkaline immersion when using glass cullet as fine aggregates. The incorporation of CAC could decrease the expansion to less than 1000 με even after 14 days of alkaline immersion. The ASR expansion decreased with the increase of CAC content up to 20%. That was due to several reasons. Firstly, aluminum (Al) in CAC was incorporated in the AAC matrix with tetrahedral and octahedral units. The tetrahedral unit increased with the increase of CAC content, which required more Na ions to balance the excessive charge. Therefore, the alkalinity of the pore solution decreased and the ASR expansion decreased consequently. Besides, more AAC gel was formed due to the CAC incorporation, which decreased the alkalinity of the pore solution as well. But further increase the CAC content (25%) increased the ASR expansion, which might be due to the formation of zeolite that decreased the strength of AAC mortars.

Brucite-Aragonite Precipitates as Weathering Products of Historic Non-MgO-Based Geomaterials

This paper analyses the mineralogical composition, texture, and structure of a stalactite sampled from the city-wall storerooms of the Nueva Tabarca fortress (southeast Spain). This speleothem presents an uncommon mineral assemblage: aragonite, brucite, gypsum, silica, and halite. Internally, it shows complex structure: (1) a central soda-straw composed by aragonite; (2) an external puff-pastry cone-crust formed preferentially by aragonite and brucite; and (3) an internal branching of coralloids, showing a subtle layering between brucite and aragonite. Gypsum, halite, and silica locate in the outer coating of the cone-crust. The sequent mineral precipitation sequence has been established: aragonite > brucite > gypsum/silica > halite. Speleothem formation is directly related to the chemical weathering of the rocks and mortars used as building materials of the city-wall. Brucite precipitates has been always linked to the presence of MgO-based geomaterials. However, the lack of these compounds as building materials in Nueva Tabarca fortress makes this investigation a unique example of brucite precipitation. PHREEQC calculations showed that interaction between pore waters and the minerals of mortar aggregates (dolomite, pyroxene, and amphibole) leads to rich-magnesium solutions. Evaporation modelling of lixiviated waters describes the precipitation of the mineral assemblage of the brucite-aragonite speleothems.

Effectiveness of using rubber waste as aggregates for improving thermal performance of plaster-based composites

In this paper, rubber waste is added to plaster-based composite to produce an alternative construction material. The main goal of this study is to investigate the effectiveness of using shredded rubber waste as aggregates in plaster mortar for improving its insulating aspect potential. This composite is obtained by mixing dune sand, plaster, rubber particles, and water. The rubber aggregates are incorporated in mixes as a partial replacement by volume of some parts of sand. Unit weight, capillary absorption of water, mechanical, and thermal-related properties are evaluated and compared according to the percentage of rubber in the mix. The results obtained showed that the addition of rubber will modify the properties of the mortar. Even though the mechanical strength is decreased with the increase of rubber content, it should be mentioned that rubber particles could significantly reduce the weight the material, decrease the rate of water absorption, and improve the insulation aspect of the composite. It can be noted that, below 50% of rubber, modeling by auto-coherent homogenization confirms the experimental results of thermal conductivity. Finally, it should be noted that recycling of rubber waste can produce an alternative eco-friendly material.

Experimental investigation on bond-slip behavior of selfconsolidating rubberized concrete

Reducing the industry’s impact on the environment is the goal of sustainable construction which can be achieved by using renewable and recyclable resources such as scrap tire waste. Great potential of this waste is found in construction mostly as a partial replacement of mineral aggregate in concrete and mortars, asphalt mixtures and geotechnical works. Previous studies on the selfconsolidating rubberized concrete (SCRC) are mostly concerned with mechanical properties of rubberized concrete. However, in order to allow structural application, it is also necessary to investigate bond-slip behavior of SCRC and reinforcement bars. Thus, in this paper pull-out tests are performed on 24 cubic samples with reinforcement confinement. Three different SCRC mixtures are made, first with concrete without rubber particles as reference mixture, second with 10%, and third with 15% rubber particles and 5% silica fume. The other parameter varied is diameter of steel bars (∅12, ∅16, and ∅20 mm). From the results obtained in experimental investigation, key bond parameters and failure modes of SCRC are compared with bond-slip behavior of self-consolidating concrete (SCC).

Recycled aggregate mortar enhanced by microbial calcite precipitation

The reuse of construction and demolition waste (CDW) is hampered by its high water absorption and weak bonds with new cement paste. This problem is more severe for recycled fine aggregates (RFAs) that are involuntarily generated during the production of recycled coarse aggregates. To explore the feasibility of reusing RFAs in construction, microbial carbonate precipitation (MCP) is presented in this study to consolidate the RFAs derived from CDW. The effects of calcium sources on bacterially induced MCP were investigated, and the efficiency of MCP for improving RFAs was evaluated in terms of physical and mechanical properties. Results show calcium chloride is an optimal calcium supplement that is useful for generating calcium carbonate, as compared with the effect of calcium nitrate. MCP treatment has improved the quality of RFAs, with decreases in water absorption, crushing value and the powder content. Furthermore, mortars containing 100% treated RFAs exhibited better workability and improved compressive strength, with a maximum increment of 32% after 28 d of curing. The pore structures of mortars containing modified RFAs were densified, with decreased porosities detected by the mercury intrusion porosity method. X-ray diffraction and scanning electron microscopy revealed the precipitation of calcium carbonate on the RFAs.

Mechanical Behavior of Masonry Mortars Made with Recycled Mortar Aggregate.

Recycling is an important habit to avoid waste. This paper evaluates the performance of masonry mortar, elaborated by replacing natural sand with recycled fine aggregate (RFA) obtained from mortar. Five families of mixtures were prepared with different replacement proportions: 20%, 40%, 60%, and 100%. A 1:4 volumetric cement-to-aggregate ratio was used for all mixtures by experimentally adjusting the amount of water to achieve the same consistency of 175 ± 5 mm. The effects of the following procedures were analyzed: (1) the use of a deconstruction technique to collect the RFA, (2) pre-wetting of the aggregates, and (3) the use of a commercial plasticizer. Experimental results show that it is possible to use this type of recycled fine aggregate as a substitute for natural sand by up to 60% in the manufacture of masonry mortar without significantly affecting its properties.

A probabilistic upscaling of microstructural randomness in modeling mesoscale elastic properties of concrete

We present a modeling framework for propagating the uncertainty, stemming from random heterogeneity of concrete microstructure, to its mesoscale elastic properties at the level of statistical volume element. The microstructure of concrete is modeled as a three-phase composite, consisting of aggregates (inclusions) in mortar (matrix), and interfacial transition zone (ITZ), a thin high porosity zone surrounding aggregates. There is inherent randomness in the composition and mechanical properties of these constituents, which in turn causes spatial heterogeneity in the local material behavior. We present a statistical characterization process to quantify the uncertainty associated with local aggregate volume fraction and aggregate size distribution. We then adopt and test a probabilistic model based on the random matrix theory and maximum entropy principle to construct a stochastic description for bounded apparent elasticity tensors at the mesoscale level, in which the bounds are obtained through a computational calibration process based on the theory of micromechanics and numerical homogenization. The framework provides an efficient way to model and simulate the local statistical fluctuations of material properties that are linked to phenomena occurring at the subscale level of heterogeneity.

Partial replacement of copper slag with treated crumb rubber aggregates in alkali-activated slag mortar

Copper slag (CS) is an industrial waste, which is generally disposed of in landfills, posing threats to the environment. Alternatively, it can be used as natural aggregate replacement in concrete/mortar, however, it results in a significant increase in material density, production and handling cost. The use of crumb rubber in combination with CS can overcome these problems, but there was no prior study on effect of such combination on the properties of alkali activated mortars (AAMs). The primary aim of this study is to address the problem stated above by replacing CS with 5, 10, 15% (by volume) crumb rubber in alkali-activated slag mortars. Furthermore, the effect of pre-treatment of crumb rubber aggregates with sodium hydroxide (NaOH) solution for 1 h and 24 h on workability, compressive strength, flexural strength, water absorption, thermal conductivity, and microstructural properties of mortar mixes was investigated. Based on the test results, the use of crumb rubber resulted in inferior workability and mechanical strength, but better thermal insulating capability as compared to the control mix. Alkali treatment promoted the rubber-binder bond and effectively enhanced the strength of mixes, especially at an early-age (up to 59%), however, alkali treatment for 24 h drastically reduced the workability of fresh mix. Thus, it is recommended to use 10% crumb rubber pre-soaked in NaOH solution for 1 h to achieve acceptable performance. Finally, the economic and ecological analysis results revealed that the produced mortar is beneficial to the environment.