Year Of Curing Research Articles

A study on fresh, mechanical, and thermal properties of limestone calcined clay cement (LC3) blended with cementitious materials

In light of environmental concerns about cement manufacture, limestone and thermally activated kaolinitic clays are being explored as supplementary cementitious materials with the potential to reduce CO2 emissions and energy usage. The use of calcined clay and limestone for clinker replacement to create a tertiary blend called limestone calcined clay cement (LC3) is one of the most promising emerging technologies for meeting environmental requirements. This paper reports on the evaluation of the fresh-state and hardened properties of cementitious pastes and self-compacting concretes (SCC) prepared using the concrete equivalent mortar method made with LC3 systems containing 30%, 35%, and 40% metakaolin (LC-30MK, LC-35MK, and LC-40MK) in comparison with ordinary Portland cement (OPC). Paste and concrete equivalent mortar specimens were prepared to investigate water demand, setting time, and workability (mini-slump flow test). Also, the compressive strength and drying shrinkage after 7 and 28 days, as well as thermal conductivity after one year of curing, were examined. The obtained results showed that the incorporation of metakaolin resulted in increased water demand to reach normal consistency. The setting time of LC3 mixtures also increased, while the same workability behavior was observed for all mixtures. LC-30MK can provide compressive strength that is comparable to OPC, especially after the first few days of curing. However, the compressive strengths of LC-35MK and LC-40MK are lower than those of OPC. Nevertheless, they demonstrate noteworthy strength characteristics. All LC3 mixtures exhibited relatively low drying shrinkage and reduced thermal conductivity compared to the OPC mixture.

Aspekti prikladnosti trostupanjskog miješanja gotove betonske smjese

Several studies have indicated that three-stage mixing (TM) methods improve the mechanical strength and slump of concrete compared to those of normal mixing methods, particularly when a recycled concrete aggregate is used. However, most studies did not address the technological aspects of ready-mixed concrete, including continuous mixing during site delivery. In this study, the properties of concrete (slump and compressive strength) based on the time lapse after mixing via the TM method (i.e. immediately, 45 min, and 90 min after mixing) were investigated, and the samples were tested after three years of curing. The results indicate some positive effects of TM on ready-mixed concrete and its characteristics on a delivery to the construction site, particularly a less severe loss of consistency compared to that of conventional mixing, as well as a positive effect on the compressive strength when fly ash is used as an aggregate coating additive in the first stage of concrete mixing.

Study of the impact of sediments on the mechanical behavior of concrete and towards the penetration of carbon dioxide

Dam reservoirs are exposed to a loss of water storage capacity due to the phenomenon of siltation. This particularity can be expressed by the siltation of reservoirs and the entrainment of particles transported by watercourses. Siltation of reservoirs is a critical state which causes a reduction in the storage capacity of dams. Algeria is characterized by a semi-arid climate, which annually loses a considerable volume of water storage. The carbonation of concrete is influenced by a number of parameters which accelerate its kinetics. These parameters are the porosity of the concrete, the quantity of lime contained in the cement, the concentration of CO2 in the atmosphere and the humidity of the environment. It should be noted that, water being the vector for moving aggressive agents, carbon dioxide can only diffuse through the concrete if the latter is not completely saturated and not perfectly dry at the same time. Another factor increasing the permeability of concrete is the amount of limestone added to the cement during its manufacture at the factory. This permeability allows the diffusion of CO2 or other aggressive agents in the concrete. The addition of limestone to cement must therefore be used with caution. The objective is to propose economically competitive and easy-to-implement formulations which allow the valorization of these materials in the making of ordinary concrete by partial substitution of cement (10, 20 and 30%) and its influence on the progress of long-term carbonation after six years of curing in the open air. The sediment is treated by calcination at 750°C to make it active. Natural carbonation tests were carried out on the study concretes in order to evaluate their durability. The results obtained confirmed the possibility of producing concretes incorporating calcined sludge at dosages of up to 30% without compromising the quality of these concretes from the point of view of behavior in the face of attacks by the dissolution of carbon dioxide from the air in the interstitial solution of concrete, meeting economic, ecological and technological objectives.

Chemo-thermo-hydro-mechanical behavior of a cement-stabilized rammed earth wall in interaction with the environment and underground soil

This work presents a numerical investigation into the structural behavior of a newly built cement-stabilized rammed earth (CSRE) wall and its interaction with the underground soil and environment. Finite element simulations were used to obtain the results, which show that the average degree of cement hydration of the wall increases annually, with the rate of increment decreasing over time. Even after five years of curing, the cement is not completely hydrated. In the first year after construction, the degree of cement hydration is higher near the indoor side of the wall compared to the parts near the outside and underneath the ground due to the higher indoor temperature. The upper and indoor sides of the wall are generally drier than the lower and outdoor sides. Rising damp water that does not evaporate in time stores as a water source in the wall, making the wet areas expand in the following days. The average wall temperature first increases due to the hydration heat and later varies seasonally with the environment. Water has a significant impact on the thermal insulation qualities of the wall. The thermal insulation of the wall decreases due to rising damp but increases owing to water evaporation. The compressive strength of the wall is mainly controlled by cement hydration at an early age but is also impacted in the later four years by the humidity of the environment and the underground soil. The higher portion of the wall loses its strength later than the lower part since it takes longer for water to reach the upper side from the ground soil. This delay is dissipated on the wall surface owing to sufficient contact with the air. The shortage of water on the upper side of the wall leads to the hydration process in this area being governed chiefly by temperature.

The Effect of the Type of Activator Anion on the Hydration of Ground Granulated Blast Furnace Slag.

In this study, ground granulated blast furnace slag was activated with a wide variety of sodium salts to compare the effects of their pH and anion size on the hydration progress and compressive strength development of GGBFS pastes. Research was carried out on samples activated with twelve different sodium salts and cured for one year. Changes in their phase composition (XRD), loss on ignition at different temperatures, expansion and microstructure (SEM + EDS) were examined over the entire curing period. The results showed that the presence of sodium ions is more important than the pH of the system, as activation took place even in the case of compounds whose solutions are characterized by a low pH, such as sodium tartrate or phosphate. The compressive strength of the pastes ranged from approximately 8 to 65 MPa after one year of curing.

Effect of different parameters on cyclic triaxial response of biopolymer treated soil

Generally, silty sand possesses very negligible cohesion and may fail under dynamic loading due to liquefaction. To mitigate liquefaction, treatment using biopolymers are now becoming popular. In the current study, liquefaction mitigation using agar biopolymer has been studied in detail. The effect of treatment parameters like agar content (0%, 0.5%, 1%, 2% and 3%) and curing period (1 day, 3 days, 7 days, 28 days and 1 year) have been studied and the effect of loading condition by varying the over consolidation ratio (1, 2, 3 and 4) were investigated by performing a series of consolidated undrained cyclic triaxial tests. The test results were analyzed to study the influence on pore water pressure, cyclic stress path behaviour and hysteresis response. It was seen that the excess pore pressure buildup was reduced with an increase in agar dosage and an increase in OCR. However, it increased with an increase in the curing period, though the maximum excess pore pressure ratio after 50 loading cycles was just 0.7 after 1 year of curing. The stiffness of the soil increased with an increase in agar content, curing period and OCR, as indicated by the higher inclination of the hysteresis loops.

Fabrication of sustainable magnesium phosphate cement micromortar using design of experiments statistical modelling: Valorization of ceramic-stone-porcelain containing waste as filler

Magnesium phosphate cement (MPC) is a potential sustainable alternative to Portland cement. It is possible to lower the total CO2 emissions related to MPC manufacturing by using by-products and wastes as raw materials. When by-products are used to develop MPC, the resultant binder can be referred to as sustainable magnesium phosphate cement (sust-MPC). This research incorporates ceramic, stone, and porcelain waste (CSP) as a filler in sust-MPC to obtain a micromortar. Sust-MPC is formulated with KH2PO4 and low-grade MgO (LG-MgO), a by-product composed of 40–60 wt% MgO. CSP is the non-recyclable glass fraction generated by the glass recycling industry. The effect of water and CSP addition on the mechanical properties of sust-MPC was analyzed using design of experiments (DoE). A statistical model was obtained and validated by testing ideally formulated samples achieved through optimization of the DoE. The optimal formulation (15 wt% of CSP and a water to cement ratio of 0.34) was realized by maximizing the compressive strength at 7 and 28 days of curing, resulting in values of 18 and 25 MPa respectively. After one year of curing, the micromortar was physico-chemically characterized in-depth using backscattered scanning electron microscopy (BSEM-EDS) and Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR). The optimal formulation showed good integration of CSP particles in the ceramic matrix. Thus, a potential reaction between silica and the K-struvite matrix may have occurred after one year of curing.

The Influence of Ambient Temperature on High Performance Concrete Properties.

This paper presents the results of tests on high performance concrete (HPC) prepared and cured at various ambient temperatures, ranging from 12 °C to 30 °C (the compressive strength and concrete mix density were also tested at 40 °C). Special attention was paid to maintaining the assumed temperature of the mixture components during its preparation and maintaining the assumed curing temperature. The properties of a fresh concrete mixture (consistency, air content, density) and properties of hardened concrete (density, water absorption, depth of water penetration under pressure, compressive strength, and freeze–thaw durability of hardened concrete) were studied. It has been shown that increased temperature (30 °C) has a significant effect on loss of workability. The studies used the concrete slump test, the flow table test, and the Vebe test. A decrease in the slump and flow diameter and an increase in the Vebe time were observed. It has been shown that an increase in concrete curing temperature causes an increase in early compressive strength. After 3 days of curing, compared with concrete curing at 20 °C, an 18% increase in compressive strength was observed at 40 °C, while concrete curing at 12 °C had a compressive strength which was 11% lower. An increase in temperature lowers the compressive strength after a period longer than 28 days. After two years of curing, concrete curing at 12 °C achieved a compressive strength 13% higher than that of concrete curing at 40 °C. Freeze–thaw performance tests of HPC in the presence of NaCl demonstrated that this concrete showed high freeze–thaw resistance and de-icing materials (surface scaling of this concrete is minimal) regardless of the temperature of the curing process, from 12 °C to 30 °C.

Mechanical properties and durability of ancient mortars in the historic buildings of Eastern Sicily

Eastern Sicily’s historic buildings are characterized by an almost uniform use of local and naturally available calcareous and lavic stone as aggregate. Also, ancient mortars comprise of lime or cement-lime binder. Very limited studies concerning the mechanical properties of the ancient mortars have been accomplished. In this paper, mortar samples collected from the surviving heritage masonry structures in eastern Sicily were selected to assess their composition. Due to limitations of dimensions, shape and cohesiveness of mortar samples collected from historic buildings, not laboratory test can be applied on the samples. Then, new mortar samples were constructed matching those of historic buildings in order to determine their mechanical properties. Hence, the restored ancient mortar, were tested after 30-60-90 days of curing and finally after 20 years of curing. The data obtained was, then compared each other. To this aim, two series of mortar were performed for a total of 400 samples. The composition of the mortars differs in according to ancient recipes determined in the laboratory by means of the chemical attack of the samples directly taken from historic buildings. The time effects as well as the aggregate (sand) influence were analyzed. To this aim bending, compression and tensile tests were carried out on all the specimens. The data obtained show after 20 years a reduction between 10 and 15% of the compressive strength in mortar studied. All of these data could be very useful for creating compatible mortar recipes for restoration works as well as to define mechanical features of ancient mortar in modeling process.

Properties of mortars based on β-belite-metakaolinite-hydrated lime binder system

A novel β-belite cement was prepared, characterized (by chemical and phase composition, particle size distribution, bulk density, specific surface area) and incorporated into mortars based on a mixed binder β-belite-metakaolinite-hydrated lime with different contents of β-belite cement (0, 20, 40, 60, 80 and 100 wt.%). The metakaoline:hydrated lime weight ratio of 1:1 and binder:sand weight ratio of 1:3 were observed in all mortars. The effect of the β-belite cement fraction on the properties of fresh mortars (water:binder ratio needed to achieve the required mortars consistency and initial setting time), on the phase composition (X-Ray diffraction phase analysis and thermogravimetric analyses) and on the structural properties of mortars (compressive strength, flexural strength, bulk density, water absorption, water absorption coefficient, shrinkage) over 1 year of curing was investigated. Freeze and thaw resistance of the mortars after 1 year of curing was also evaluated. Partial replacement of metakaolinite-hydrated lime binder with β-belite cement affected all investigated mortar properties. Significant improvements in mechanical properties and resistance to freezing and thawing cycles were the main advantages.

Changes of bond strength properties of hot-dip galvanized plain bars with cement paste after 1 year of curing

This paper studies the effect of the corrosion of hot-dip galvanized steel on the porosity development of cement paste at the interfacial transition zone (ITZ) between the two materials. The corrosion of hot-dip galvanized steel by hydrogen evolution was studied during the curing of cement paste samples stored above the water level (AW = 95% RH) and below the water level (BW). The changes in the corrosion process were recorded via the time – open circuit potential evolution (Ecorr/FeCr18Ni9) of stainless steel plate (recounted to Ecorr/SCE) in cement paste bodies. Total monitoring time for the development of both parameters were 6 days, 4 months and 1 year.Further, the bond strength between plain hot-dip galvanized steel and cement by modified pull-out test was verified. Total time of curing was in this case 6 days, 4 months and 1 year.The corrosion reaction between hot-dip galvanized steel and fresh cement produces hydrogen, which significantly increases the capillary porosity of the cement paste at the interfacial transition zone (ITZ). The resulting capillary pores are not effectively filled by the zinc corrosion products and the porous structure is maintained even after one year of curing.Porosity increase of cement consequently results in reduction of bond strength between plain hot-dip galvanized steel and concrete which remains low even for samples cured for very long exposure time.

The effect of doum palm fibers on the mechanical and thermal properties of gypsum mortar

The main objective of this paper is the evaluation of the possibility of using a gypsum mortar reinforced with doum palm fibers as thermal insulators in building material. Several composite configurations with three sizes and five-weight ratios (from 0.5% to 2.5%) of doum palm fiber were prepared for mechanical and thermo-physical characterization. Generally, natural fibers are affected by the alkali environment of gypsum mortar. To overcome this problem, doum palm fibers were treated with a NaOH solution of 1% concentration to enhance their resistance against chemical degradation. Chemical treatment of fiber removes some hemicellulose and lignin and tends to make the fiber more homogenous, which enhances fiber–matrix interfacial properties. In addition, the mechanical properties of the specimens were tested after 7 days, 28 days and 1 year of curing in normal conditions. The obtained results show an improvement in the mechanical performance of composites reinforced with treated fibers. In fact, better results were obtained for gypsum mortar reinforced with treated reinforcement seive2 for the value of 1% of fibers. It was also noticed that NaOH treatment has an influence on the thermal conductivities. In fact, the use of treated doum palm fibers as reinforcement in gypsum mortar seems to be an alternative natural material to be used as a thermal insulator material.

Mine Backfilling in the Permafrost, Part I: Numerical Prediction of Thermal Curing Conditions within the Cemented Paste Backfill Matrix

The mechanical behavior of cemented paste backfill (CPB) in permafrost regions may depend on the thermal curing conditions. However, few experimental data are available for calibrating and validating numerical models used to predict these conditions. To fill this gap, a three-dimensional (3D) laboratory heat transfer test was conducted on CPB placed in an instrumented barrel and cured under a constant temperature of −11 °C. Results were used to calibrate and validate a numerical model built with COMSOL Multiphysics®. The model was then used to predict the evolution of the temperature field for CPB cured under the thermal boundary conditions for a backfilled mine stope in the permafrost (at −6 °C). Numerical results indicated that the CPB temperature gradually decreased with time such that the entire CPB mass was frozen about five years after stope backfilling. However, the permafrost equilibrium temperature of −6 °C was not reached throughout the entire CPB mass even after 20 years of curing. In addition, the evolution of the temperature field in the permafrost rock showed that the thickness of the thawed portion reached about 1 m within 120 days. Afterwards, the temperature continues to drop over time and the thawed portion of the permafrost refreezes after 365 days.

Durability of cement pastes exposed to external sulfate attack and leaching: Physical and chemical aspects

Sulfate ions in seawater or underground can attack the cement paste leading to expansion and strength loss. This expansion is usually related to ettringite and gypsum precipitation. This study aims to characterize the possible altered zone and to identify the mechanisms of degradation under such conditions. For this study, cement pastes manufactured using CEM I with two w/c ratios (0.45 and 0.60) were exposed to sodium sulfate solutions (semi-immersion at a controlled pH = 8.0 ± 0.1) after one year of curing in water. The analysis of the physical aspect of this phenomenon shows that two modes of transfer occur: transfer of sulfate ions to the cement matrix and leaching of calcium ions to the external solution. The analysis of the chemical composition of the affected material highlights the progressive consumption of portlandite at the surface, the decalcification of C-S-H and the formation of AFt from both Afm and aluminium incorporated in C-S-H.

Generalized Fracture Toughness and Compressive Strength of Sustainable Concrete Including Low Calcium Fly Ash.

The paper presents the results of tests on the effect of the low calcium fly ash (LCFA) addition, in the amounts of: 0% (LCFA-00), 20% (LCFA-20) and 30% (LCFA-30) by weight of cement, on fracture processes in structural concretes. In the course of the experiments, compressive strength of concrete and fracture toughness for: I (tensile), II (in-plane shear) and III (anti-plane shear) models of cracking were measured. The tests determined the effect of age of concretes modified with LCFA on the analyzed parameters. The experiments were carried out after: 3, 7, 28, 90, 180 and 365 days of curing. Fracture toughness of concretes was determined in terms of the critical stress intensity factors: , , and then a generalized fracture toughness was specified. The obtained results are significant for the analysis of concrete structures subjected to complex loading. The properties of composites with the additive of LCFA depend on the age of the concrete tested. Mature concretes exhibit high fracture toughness at 20% additive of LCFA, while the additive of LCFA in the amount of 30% weight of cement has a beneficial effect on the parameters of concrete only after half a year of curing.

Chemical, mineralogical and petrographic characterization of Roman ancient hydraulic concretes cores from Santa Liberata, Italy, and CaesareaPalestinae, Israel

Periodico di Mineralogia (2011), 80, 2, 317-338 - DOI:10.2451/2011 PM0023 Chemical, mineralogical and petrographic characterization of Roman ancient hydraulic concretes cores from Santa Liberata, Italy, and Caesarea Palestinae, Israel Gabriele Vola 1,* , Emanuele Gotti 1 , Chris Brandon 2 , John P. Oleson 3 and Robert L. Hohlfelder 4 1 CTG Italcementi Group, Lab Dept., Via Camozzi, 124 - 24121 Bergamo, Italy 2 Pringle Brandon Architects, 10 Bonhill St, London, EC2A 4QJ, UK 3 Departmentt of Greek and Roman Studies, University of Victoria, Victoria BC V8W 3P4, Canada 4 Departmentt of History, University of Colorado, Boulder, CO 80309-0234, USA *Corresponding author: g.vola@itcgr.net Abstract This study reports chemical, mineralogical and petrographic characterization of ancient hydraulic concretes from the Roman piers at Santa Liberata Orbetello (Grosseto) Italy (~50 B.C.), and breakwaters at the harbour of Caesarea Palestinae, Israel (c. 25 B.C.), drilled by the ROMACONS (Roman Maritime Concrete Study) team in 2003-2005. Both sets of concrete contain a pozzolanic sanidine- and clinopiroxene-bearing tuff, identified as coming from the pyroclastic deposits of the Phlegrean Fields (Naples), the so-called pulvis Puteolanus of Vitruvius. However, the content of tuff changes, being predominant at Santa Liberata, whereas it is only a smaller fraction of the total aggregate at Caesarea that is mostly composed of local kurkar calcareous sandstone, with occasional ceramic fragments. The cementitious binding matrix presents amorphous gel-like, silica-rich C-A-S-H, with subordinated sparry calcite cement, and unusual dull white grains composed of calcite, tobermorite, and ettringite, apparently derived from reaction with hydrated lime in seawater. Saline encrustations, from the diffusion of chlorides and sulphates, and characteristic authigenic spherical zeolites with the rosette texture also occur within the mortar's porosity. These new data put further constraints on the various reactions occurring in roman concretes in over two thousand years of curing in an aggressive marine environment. Key words : Ancient Roman harbours; hydraulic seawater concretes; pozzolanic mortars; pulvis Puteolanus of Vitruvius; ROMACONS project; Neapolitan Yellow Tuff (NYT).

Early-Age Structural Properties of Base Material Treated with Asphalt Emulsion

The objectives of this research were to investigate the early-age structural properties of base materials stabilized with asphalt emulsion and to assess the rate at which emulsion-treated base (ETB) design properties are achieved. Three experimental sections were established along a pavement reconstruction project near Saratoga Springs, Utah. Field tests were performed to assess the structural properties of the ETB immediately after construction and at 2, 3, 7, and 14 days; 4 months; and 1 year. Measured values were plotted against time to determine trends in ETB strength development and to determine pavement capacity. Modulus values were consistently low in all three sections during the first 2 weeks after construction, increased dramatically by 4 months, and then decreased considerably by 1 year. In the first 2 weeks after construction, the average ETB structural coefficient was 0.04. Only two of the three sections reached the design structural coefficient of 0.25, which occurred after approximately 3 months; however, the average structural coefficient measured for all three sections after 1 year of curing, which included a winter, was only 47% of the design strength. The results of this research showed that, while pavement capacity was sufficient at 4 months, it was severely reduced during the first 2 weeks and at 1 year. Trafficking under these reduced capacities would be expected to greatly compromise long-term pavement performance. For this reason, trafficking of materials similar to those investigated in this research is not recommended during at least the first 2 weeks after construction.

Influence of recycled aggregates on long term mechanical properties and pore size distribution of concrete

Abstract This paper presents the results of a study of the long term mechanical properties and pore structures of recycled aggregate concrete. In this study, two different sources of recycled aggregates were used to replace natural aggregate at a level of 100%. The compressive and splitting tensile strength of the concrete were tested, and the pore structures of the concrete were analyzed. The results showed that after 5 years of curing, the recycled aggregate concretes had lower compressive strength and higher splitting tensile strength than the corresponding natural aggregate concrete. However, from 28 days to 5 years, the increase of compressive and splitting tensile strengths was more in the recycled aggregate concretes. After 5 years of curing, the concrete made with 100% of crushed old concrete aggregate had the lowest porosity. Good correlations were found between compressive and tensile strength and porosity.

Mechanical properties of 5-year-old concrete prepared with recycled aggregates obtained from three different sources

The current paper presents the findings of a long-term study on the mechanical properties of concrete prepared with recycled aggregate obtained from three different sources. The concrete mixtures were prepared with a cement content of 355 kg/m3 and water-to-cement (w/c) ratio of 0·55. The recycled aggregate was used as 0, 20, 50 and 100% replacements of natural aggregate. It was found that after 5 years of curing, the compressive strength and modulus of elasticity of the concrete made with recycled aggregates decreased with an increase in recycled aggregate content. Starting from the curing age of 1 year, however, the splitting tensile strengths of the concrete prepared with 100% recycled aggregate were higher than that of the natural aggregate concrete. The gain in strength and elastic modulus over time of the concrete prepared with recycled aggregates derived from pure crushed concrete was higher than the corresponding natural aggregate and recycled aggregates derived from other construction and demolition wastes. This is attributed to the improvement in bonding between the new cement matrix and the old recycled aggregates.

Formulation et caractérisation de bétons bas pH

ABSTRACT Investigations were carried out to formulate and characterize low-alkalinity and low-heat cements which would be compatible with an underground waste repository environment. Pozzolans (high-silica product such as fly ash and silica fume) and blast furnace slag were added to Portland cement to decrease the cement pore solution pH to 11. The alkali content of the interstitial solution (≈ 1 to 5 mmol/L) of blend was strongly reduced which decreased the pH by more than one unity as compared with control samples. The blends exhibited a low heat output (temperature rise below 20°C). The prepared concrete specimens had a compressive strength higher than 70 MPa after one year of curing in 100% RH, a low shrinkage (−350 to −500μm/m) and it was possible to prepare workable concrete despite the very high amounts of pozzolans in the blends.