Total Binder Mass Research Articles

Mix design, optimisation and performance evaluation of three-dimensional printable concrete

Three-dimensional (3D) concrete printing (3DCP) is a cutting-edge construction method that has recently received much attention. Most 3DCP research studies have focused on printer development, printable material mix designs and the complexity of geometry shapes. This research study primarily focused on determining appropriate mix proportions and suitable 3D-printable concrete (3DPC) mix designs using a trial-and-error approach. Experimental tests were carried out on 27 trial mixes made with different materials to determine printable properties such as flowability, buildability, extrudability and open time. Printed and cast samples were tested for compressive strength. The 3DPC mix with 19% ordinary Portland cement, 23% fly ash, 7% silica fume, 13% ground granulated blast-furnace slag, 4% limestone and 0.22% superplasticiser (% by mass of total binder) was found to be an ideal mix proportion, exhibiting the required 3DPC characteristics such as good buildability, easy extrusion, low setting time, mix cohesiveness and reduced deformation. The proposed mixing protocol and the suggested 3DPC mix design are encouraging for large-scale 3DCP. To demonstrate the application of the 3DPC mix, 3D-printed concrete furniture was fabricated with a nozzle of size 30 mm, an extrusion speed of 100 mm/s and a printing speed of 60 mm/s.

Determination of the stiffness of ecological asphalt mixtures with non-destructive impact resonance tests

The objective of this study is to characterize the linear viscoelastic behavior of ecological asphalt mixtures with non-destructive impact resonance testing. Two specimens of each of the four investigated mixtures were produced and tested in laboratory: a reference mixture (REFMIX), a mixture containing a modified binder with 30% of Kraft lignin in mass of total binder (LIGNIN), a mixture with 20% of reclaimed asphalt pavement (RAP) in mass of total aggregates (RAP20), and a mixture with 50% of RAP (RAP50). The specimens were tested at five temperatures (-20 °C, 0 °C, 10 °C, 20 °C, and 30 °C) with an impact resonance equipment to obtain experimental Frequency Response Functions (FRF’s). Subsequently, a back-calculation procedure was used to determine two linear viscoelastic properties (absolute value and phase angle of the complex modulus) from FRF’s measurements using finite element method (FEM) simulations. The results indicated a good repeatability of the test, with results from all specimens presenting the same trend, a decrease of the modulus and an increase of the phase angle with increasing temperature. Results also showed that the modified mixtures are stiffer than the reference mixture at each temperature. Kraft lignin has the greatest influence in increasing the stiffness in comparison with the reference mixture, followed by the addition of 50% and 20% of RAP. It was concluded that the addition of ecological materials, such as lignin and RAP, directly affects the viscoelastic behavior of bituminous materials, which can be beneficial for many applications.

Study on Mechanical and Microscopic Properties of Fly Ash Cement‐Based Materials in High Geothermal Environment

Through simulating a hot and humid environment of high‐ground‐temperature tunnel and taking advantage of mechanics performance testing, differential thermal analysis (DTA) technology, and scanning electron microscope (SEM) observation technology, the macroscopic and microscopic properties of cement‐based materials and their performance improvement measures can be investigated. Also, the mechanism of improvement can be revealed from the perspective of the hydration degree and microstructure. The experimental results indicate that under the hot and humid environment of high ground temperature, adding fly ash could efficiently weaken the early high‐temperature curing effect of cement‐based materials, improving their physical properties. But the mechanical strengths of cement‐based materials go through a transformation from increase to decline with the rise of fly ash, appearing a maximum value in the process. Meanwhile, the differential thermal analysis and the microstructure analysis show that a hot and humid environment enhances the pozzolanic activity of fly ash and an appropriate ratio of fly ash could improve the microstructure of cement slurry, but when fly ash covers more than 30% of the mix of cement‐based materials, the quantity of the alkaline exciting agent, calcium hydroxide, is not enough to meet the needs of the active effect of fly ash and the hydration degree of fly ash becomes extremely low. Last, under a hot and humid environment of high ground temperature, fly ash saturation in cementing material should range from 20% to 30% in mass of total binder, which makes for long‐term performance of cement‐based materials.

Effect of type and content of expansive agent on performance of fiber-reinforced concrete with adapted rheology

A performance-based mixture design approach was utilized to optimize the binder content and composition for fiber-reinforced super workable concrete (FR-SWC) and fiber-reinforced self-consolidating concrete (FR-SCC). The test parameters included the replacement ratio of the cement by a Class C fly ash (FA), type and content of expansive agent (EA), and total binder content. Hooked-end steel fibers measuring 30 mm in length were used at 0.5% by volume. The investigated concrete was tested for slump flow, modified J-ring, sieve stability, bleeding, visual stability index, air content, unit weight, as well as compressive and splitting tensile strengths. The elastic modulus, autogenous, drying shrinkage, and restrained shrinkage were determined for optimized mixtures. The optimized binder content for the FR-SCC mixtures was 475 kg/m3 with 30% FA replacement, by mass of total binder. For the FR-SWC mixtures, the binder content was 380 kg/m3 binders with 30% FA, by mass. In both mixture types, a Type-G EA was incorporated at 4% by binder mass.Test results indicated that a sharp loss in filling ability was obtained in mixtures made with a Type-K EA compared to those made with a Type-G or no EA. The coupled used of fibers and EA resulted in a slight increase in compressive strength for the FR-SCC but considerable improvement in compressive strength (up to a 50%) in the case of FR-SWC. The FR-SCC and FR-SWC mixtures exhibited up to 55% and 80% greater splitting tensile strength, respectively, compared to the non-fibrous concrete. The combination of steel fiber and EA significantly reduced shrinkage, up to 65% lower shrinkage after one year for the FR-SCC and FR-SWC mixtures. An increase in restrained shrinkage resistance was observed when the EA or fiber was used in proportioning the FR-SCC. Combined use of fibers and 4% Type-G EA led to the highest reduction in cracking potential that decreased from relatively high to low level with the time-to-cracking increasing from 12.5 to 36.5 days.

Extensive use of waste glass in one-part alkali-activated materials: Towards sustainable construction practices.

The feasibility of the extensive recycling of waste glass in alkali-activated materials (AAMs) was evaluated. The waste glass was utilised in AAMs for two purposes: a partial activator and a mineral precursor. The waste glass was blended with commercial sodium hydroxide and then heated to produce the solid activator powder. The technical performance of waste glass-based activator was investigated to replace commercial sodium silicate, a common alkali-activator used in AAMs. The effect of waste glass using only as the activator (WGA) and using as both activator and precursor (WGAP) in fly ash/slag-based one-part AAMs was studied using strength and microstructure characterisations. A mass-cost and emission analysis of waste glass-based AAMs (WGA and WGAP) was conducted, comparing the results with ordinary Portland cement (OPC). Characterisation tests of waste glass-based activator showed the effective formation of sodium silicate minerals with the adequate dissolution of activator in water by releasing reactive alkali and silica. Both WGA and WGAP showed comparable strengths at 56days with a denser microstructure under ambient curing. According to mass analysis, waste glass could be utilised up to 17% by mass of total binder. Based on the analysis of cost and CO2 emissions, WGA and WGAP are around 23% and 15% cheaper and 84% and 82% greener than OPC. The dual role of waste glass in AAMs as an activator and as a precursor broadens the recycling of glass waste in the cement industry by favouring technical and environmental outcomes.

Hydration and mechanical properties of UHPC matrix containing limestone and different levels of metakaolin

In this paper, the hydration process and mechanical properties of UHPC matrix incorporated with limestone (LS) and different substitution rates of metakaolin (MK) were investigated. MK was added with five levels of substitution (0, 5%, 10%, 15% and 20%) and LS was kept at 30% of the total binder mass. Mechanical properties, hydration heat, hydration products and pore structure measurements were carried out for every mixture. The results show that the hydration rate as well as the hydration heat peak of UHPC pastes decrease with MK level in the first 24 h possibly due to the higher superplasticizer usage, but the hydration process is accelerated with the incorporation of MK after 24 h. The pozzolanic reaction of MK and synergistic effect with LS consumes portlandite and induces the formation of more CSH gels with the improved microstructure of UHPC matrix. The trace of calcium monocarboaluminate (Mc) phase can be observed in UHPC paste samples with a low MK substitution (5%), and becomes weaker with the higher MK dosage. The pozzolanic reaction of MK with replacement level of 15% results in the best long-term compressive strength of UHPC mortars. Therefore, the incorporation of both MK and LS at an optimal level is favorable to manufacture UHPC with improved mechanical properties.

Permeable Nanomontmorillonite and Fibre Reinforced Cementitious Binders.

Clinker reduction in cementitious binders is of paramount importance today, and nanotechnology has extended permissible limits. In the present study, a reference binder consisting of 60% Portland cement, 20% limestone, 20% fly ash, 3% polyvinyl alcohol (PVA) fibres and 2% superplasticizer is optimized with three different types of nano-montmorillonite (nMt) dispersions; two organomodified ones and an inorganic one at different proportions (0.5% to 4%). Flexural strength, measured on day 7, 28, 56 and 90, was improved after day 28 with the addition of inorganic nMt. Thermal gravimetric analyses carried out on day 7, 28, 56 and 90 coupled with x-ray diffraction (at day 28) showed a distinctively enhanced pozzolanic reaction. Backscattered electron imaging confirmed changes in the microstructure. Late age relative density measurements of the nMt cementitious nanocomposites showed higher values than these of the reference paste, which can be attributed to better particle packing. Mercury intrusion porosimetry measurements give support to the optimal nMt dosage, being 1% by total mass of binder and water impermeability tests (modified with BS EN 492:2012) suggest that inorganic nMt can be a viable option material where permeability constitutes a prerequisite. Suggestions for further activation of the nMt-fibre reinforced cementitious nanocomposites were also made.

Restrained Shrinkage Mechanism of Ultra High Performance Concrete

The understanding and controlling of the restrained shrinkage is critical for the application of ultra high performance concrete (UHPC). This study made an analysis of restrained shrinkage mechanism of four kinds of UHPCs based on the direct tensile test accompanied with acoustic emission (AE) source location, free shrinkage test and restrained shrinkage test. The effects of UHPC tensile properties (strain softening or strain hardening) and high performance calcium sulphoaluminate (HCSA, a new kind of expansion agent) dosages (0%, 3% and 6% by mass of total binder) were investigated. The restrained shrinkage cracking mechanism of strain hardening UHPC and strain softening UHPC was analyzed based on AE analysis method under direct tensile loading. The results indicates that strain hardening UHPC shows multiple micro-defects to relax the restrained tensile stress marginally while strain softening UHPC shows several hairline cracks to relax the restrained tensile stress evidently. In ASTM C1581-04 ring test, the restrained shrinkage of strain hardening UHPC with HCSA dosage of 0%, 3% and 6% at 80d is 141 με, 96 με and 16 με, respectively. The HCSA expansion agent can effectively reduce the restrained shrinkage of UHPC and the influence on the structure.

Thermogravimetric analysis and microstructure of alkali-activated metakaolin cement pastes

This study reports the thermogravimetric analysis and microstructure characteristic of alkali-activated metakaolin cement pastes using Na2SiO3-to-NaOH ratio of 1.5. Metakaolin was used at 70, 80, 90, 95 and 100% by total mass of binder, and Portland cement (ASTM Type I) was used at 0–30% by total mass. Alkali/binder ratio of 1.5 and water curing at 23 °C was used. Thermogravimetric analysis and scanning electron micrographs showed that at 70% metakaolin the major phase found is calcium silicate hydrate (C–S–H) which is normally found in normal water-based cement paste mixes with a slight shoulder peak of N–A–S–H. At higher metakaolin content (80% and higher), sodium aluminium silicate hydrate (N–A–S–H) phase was detected as found in geopolymer, and this is the case in 100% metakaolin mix where essentially only N–A–S–H was found. The compressive strength results were found in the region of 43–48 MPa with higher strength found at higher metakaolin content. Therefore, the results of alkali-activated metakaolin cement paste mixes showed interesting change in the major phase of C–S–H to N–A–S–H depending on amount of Portland cement and metakaolin.

Uniaxial compressive behaviors of fly ash/slag-based geopolymeric concrete with recycled aggregates

The uniaxial compressive stress-strain behaviors of fly ash/ground granulated blast furnace slag (GGBFS) geopolymeric concrete containing recycled aggregate were investigated in this study. Geopolymeric concretes with the variations of three recycled aggregate replacement ratios (i.e., 0%, 50% and 100%) and four contents of slag (i.e., 0%, 10%, 20% and 30% of the mass of total binder) were tested under uniaxial compression. Special attention was devoted to the failure behaviors and patterns, stress-strain characteristics (such as the peak stress, the elastic modulus, the peak strain, and the ultimate strain) and energy absorption capacity. The results showed that the peak stress, elastic modulus and energy absorption (toughness) decreased with the increase of the replacement ratio of recycled aggregate, while these mechanical properties increased when the content of slag increased. The reverse trend was observed with respect to the ductility. Moreover, the inclusion of slag could alleviate the nagative effects of the recycled aggregate replacement on the stress-strain characteristics of geopolymeric concrete. Additionally, a stress-strain model was developed in this study by modifying the parameters of the existing stress-strain model with the best prediction. This new proposed model can satisfactorily describe the stress-strain behaviors for both geopolymeric natural aggregate concrete and geopolymeric recycled aggregate concrete.

The Effect of Calcium Formate, Sodium Sulfate, and Cement Clinker on Engineering Properties of Fly Ash-Based Cemented Tailings Backfill

The influence of admixtures on the engineering properties of fly ash-based cemented tailings backfill (CTB) is a topic of significant practical interest, as it affects the backfilling cost and the environmental effect of mining operation. This paper presents results of an experimental study on the influence of different activators on the engineering properties of the CTB containing fly ash. CTB samples are mixed with different contents of calcium formate, sodium sulfate, and cement clinker (4%, 8%, and 12% by mass of total binder) and cured in a cubic chamber (at 20°C and RH 90 ± 5%) for 3, 7, and 28 days. Specimen tests were performed to assess the slump height, setting time, leaching water rate, vertical settlement, and strength development. Furthermore, the XRD analyses were conducted on the hydration products of fly ash-based CTB mixtures. The results show that activators can cause decrease in the slump height, leaching water rate, and vertical settlement of fly ash-based CTB mixtures. However, inclusion of cement clinker ranging from 8%–12% of total binder can reduce the slump height, setting time, leaching water rate, and vertical settlement to an acceptable range. Addition of calcium formate in the fly ash-based CTB caused negligible change in compressive strength. The compressive strength improved with higher content of sodium sulfate and cement clinker at the age of 28 days. XRD analyses showed considerable intensity counts of C-S-H gel, calcium hydroxide, and ettringite, resulting from the addition of sodium sulfate and cement clinker. This study also shows that an understanding of the effect of activators on the engineering properties of fly ash-based CTB is crucial for designing a cost-effective and workable CTB with reduced environmental impact.

Mechanical and acoustic properties of fiber-reinforced alkali-activated slag foam concretes containing lightweight structural aggregates

This experimental study aimed to develop alkali-activated slag foam concretes with good acoustic properties for the indoor walls of residential buildings. Petrit-T, which is a by-product obtained in the manufacturing of sponge iron with a fine particle-size distribution and with rich calcium content, was used to prepare the structural lightweight aggregates. The produced lightweight structural aggregates were used in the preparation of alkali-activated slag binders, wherein ground granulated blast-furnace slag (GGBFS) as the binder was activated by an alkali solution.In the first stage of this study, the effects of using different types of fibers, including Polyvinyl alcohol (PVA), polypropylene (PP), and basalt, on the mechanical properties of alkali-activated slag binders were investigated. The mechanical properties were evaluated in terms of the compressive and flexural strengths. Thereafter, to achieve the best performing fiber reinforced alkali-activated slag concrete in terms of mechanical properties, the developed fiber-reinforced composition was used to generate alkali-activated slag foam concretes using different pre-made foam dosages (10, 15, 20, 25, 30, and 35% of the total binder mass). Finally, alkali-activated slag foam concretes were developed by varying the density in the range of 0.55–1.5 g/cm3; compressive strength in the range 2.5–13 MPa; and acoustic absorption coefficients higher than 0.5 in the medium-to-high frequency regions. Moreover, the density and acoustic properties were found to be linearly correlated.

Thermal stability and evolved gas analysis of rejuvenated reclaimed asphalt pavement (RAP) bitumen using thermogravimetric analysis–Fourier transform infrared (TG–FTIR)

Several reports exist on the use of natural-oil-based materials as rejuvenators to restore the properties of aged binders—more specifically, regarding their ability to enhance the binders’ low-temperature properties and to reduce their stiffness. Rejuvenators are typically made of low molecular weight constituents which could easily volatilize and thus render the rejuvenated binder thermally unstable. Hence, the study of the thermal stability of rejuvenated binders is of paramount importance. In this research, a binder with a performance grade (PG) of PG58-28 modified with a soybean-derived rejuvenator at 12% by mass is added to an extracted reclaimed asphalt pavement (RAP) binder at a ratio of 1:5 resulting in a rejuvenator dosage rate of 2% by total mass of binder. The PG of the rejuvenated RAP binder is determined using both dynamic shear rheometer and bending beam rheometer. The thermal stability of the rejuvenator and the binders is verified using thermogravimetric analysis (TG). The rejuvenator shows good thermal stability up to a temperature of 302 °C. The RAP binder containing the rejuvenator shows similar thermal stability to the unrejuvenated RAP binder. The evolved gases from the TG analysis are analyzed using Fourier transform infrared (FTIR) to chemically characterize the rejuvenator and the binders. The FTIR spectrum of the rejuvenator reveals characteristic peaks. The intensity of these peaks serves as an indication of the rate of mass loss of the rejuvenator within the rejuvenated RAP binder.

Natural hydraulic lime versus cement for blended lime mortars for restoration works

The paper analyses the potential of blended lime-cement mortars to substitute blended lime-natural hydraulic lime mortars as repair mortars in restoration works, since the availability of natural hydraulic lime is reduced in many countries, unlike cement. The study focuses on the pore structure of both types of blended mortars and its implications on their water transport properties, initial mechanical strength and overall incompatibility risk. The influence of binder type and composition and of binder/aggregate ratio on pore structure was discussed. Cement altered more markedly the mechanical and water transport properties of blended mortars than hydraulic lime, with consequences on compatibility. Considering the properties evaluated, blended lime-cement mortars can be used but cement content should be higher than 25% (of total binder mass), so that there is a strength increase at early age, and lower than 50%, in order to not significantly affect compatibility. Nevertheless, the blended lime mortar with 50% natural hydraulic lime presented the highest potential for restoration.

Effect of mineral admixtures on fluidity and stability of self-consolidating mortar subjected to prolonged mixing time

During continuous mixing of concrete in a truck mixer for its hauling to a construction site, concrete should remain workable without any signs of instability. Good workability at construction site is essential for high quality concrete since concretes of bad workability are prone to yield low strength and poor durability properties. This paper presents the effects of water to binder ratio, binary and ternary blends use of fly ash (FA) and metakaolin (MK) on fluidity, viscosity, and stability of self-consolidating mortars (SCMs) subjected to prolonged mixing time. The obtained results indicate that, by prolonged mixing time, flocculated cement particles are dispersed and as a result, fluidity is increased and so, the risk of instability increases. In addition, increasing FA content from 0 in the reference mixture to 20% and 50% of total binder mass increased the segregation index by about 48% and 160%, respectively. Furthermore, mixtures containing MK and FA have higher fluid capacity without any signs of instability. The addition of 7.5% MK has significantly improved the overall performance of the mixture, including the segregation stability.

Influence of shrinkage-reducing admixtures on plastic and long-term shrinkage

Abstract The use of shrinkage-reducing admixtures (SRA) has been suggested to improve concrete performance in terms of lower risk of cracking related to drying shrinkage. Various forms of SRA are commercially available and they may act through different mechanisms. Some SRA mainly acts on drying and weight loss leading to shrinkage. In this paper, the influence of a liquid SRA on plastic shrinkage, long-term shrinkage, mechanical characteristics as well as concrete pore structure were investigated. Samples of concrete were prepared with two water-to-cement ratios (w/c) to design ordinary and high strength concrete. The effect of the shrinkage-reducing admixture was studied by adding 1% to the total mass of binder, while keeping the other parameters constant. At early age, the results indicate that the SRA lead to the same plastic shrinkage for w/c = 0.65 while it reduced the plastic shrinkage by 25% for w/c = 0.43. Drying shrinkage was assessed from 1 day on hardened concrete. The SRA reduced the 7 day drying shrinkage for w/c = 0.65 and w/c = 0.43 concrete mixtures by up to 56%–31%, respectively, and the 70 day drying shrinkage by up to 33%–25% when the specimens were cured for 24 h then stored at relative humidity of 50%. At equal water-to-cement ratios, the SRA is seen to be more efficient in reducing drying shrinkage at early ages. These findings suggest that the SRA is most effective when internal relative humidity is relatively high or when higher porosity exists in the material. In fact, the SRA modified the pore structure increasing the total porosity and eliminating the percentage of larger pores with diameters ranging from 300 to 1000 nm. When concerned with drying of concrete, the larger pores are the first ones to lose their internal water and consequently change the RH levels where capillary stresses are the main cause of shrinkage. Thus, this phenomenon may contribute in the reduction of drying shrinkage that occurs when this liquid SRA is used in concrete.

The effect of various slaked limes on the microstructure of a lime–cement–sand mortar

The present work aims to provide a better understanding of the effect of both the proportions and the characteristics of slaked lime on the microstructure of a lime–cement–sand mortar. Cement (CPA CEM I 52.5) has been replaced by various categories of slaked lime chosen for the diversity of their physico-chemical characteristics. Cement has been replaced by lime in proportions varying between 0 to 10% of the total binder mass. With very few exceptions, mortars were produced by maintaining the quantity of water constant. Experimental results show that it is necessary to have a high lime substitution percentage to influence the microstructure of the mortar, except in the case of a lime containing magnesium hydroxide or calcic lime featuring sizeable specific surface area. The influence of the nature of the substituted lime on the development of the microstructure in the matrix has been examined by SEM observations of the mortar micro porosity.

A study of the viscosity of lime–cement paste: influence of the physico-chemical characteristics of lime

This study has been undertaken in order to determine the influence of the proportions and characteristics of lime, and particularly the viscosity, on the properties of a cement–lime mortar. The cement (CPA CEM I 52,5) has been substituted by different types of lime: calcium and magnesium hydroxides, industrial slaked limes chosen specifically for the diversity of their physico-mechanical characteristics, such as chemical composition, specific surface and grading distribution. Some of them have been hydrated under atmospheric pressure. One of them has been hydrated under pressurised conditions and is a hydrated dolomite. The cement has been substituted by lime in a proportion varying between 0% and 100% of the total binder mass. Water is added to obtain mortars with identical consistency regardless of the nature and quantity of lime used. The consistency sought for the various pastes was precisely that of a cement paste which yields a “normal” mortar (EN 196-1), such that sand/cement=3 and water/cement=0.5. The experimental results have been analysed according to the chemical composition, the specific surface, the pore volume and the grain size distribution of the various limes. It appears that the viscosity of a cement–lime paste is more heavily influenced by the morphology of the lime than by its chemical composition.