Influence of Recycled Concrete Fine Powder on Durability of Cement Mortar

In this paper,the durability of cement mortar prepared with a recycled-concrete fine powder(RFP)was examined;including the analysis of a variety of aspects,such as the carbonization,sulfate attack and chloride ion erosion resistance.The results indicate that the influence of RFP on these three aspects is different.The carbonization depth after 30 days and the chloride diffusion coefficient of mortar containing 10%RFP decreased by 13.3%and 28.19%.With a further increase in the RFP content,interconnected pores formed between the RFP particles,leading to an acceleration of the penetration rate of CO_(2)and Cl^(−).When the RFP content was less than 50%,the corrosion resistance coefficient of the compressive strength of the mortar was 0.84-1.05 after 90 days of sulfate attack.But the expansion and cracking of the mortar was effectively alleviated due to decrease of the gypsum production.Scanning electron microscope(SEM)analysis has confirmed that 10%RFP contributes to the formation of a dense microstructure in the cement mortar.

Effect of waste concrete with different strength on mechanical properties of recycled fine aggregate mortar

The influence of source concrete (SC) with different compression strengths on the workability and mechanical properties of recycled mortar made with river sand substituted by 100% fine recycled concrete aggregates (FRCA) is experimentally investigated. The basic physical performance test shows that with the increase in SC strength, FRCA exhibit lower water absorption and crushing index, meanwhile keeping higher densities. Mechanical property tests, including compressive strength, flexural strength and uniaxial compressive stress-strain tests, show that compressive strength,flexural strength and elasticity modulus of recycled sand mortars increase roughly with the increase in SC strength. The proposed mixture design method demonstrates that all of the components can be kept as the same as those in natural mortar mixture design and FRCA must be pre-wetted before making mortar mixture. Meanwhile, the reuse of higher strength SC can ensure that recycled mortar mixtures are able to achieve similar mechanical performance when compared to natural mortar designs.

Substitution of Aggregates in Concrete and Mortar with Coltan Mining Waste: Mechanical, Environmental, and Economic Impact Case Study

The mining process involves drilling and excavation, resulting in the production of waste rock and tailings. The waste materials are then removed and stored in designated areas. This study aims to evaluate the mechanical strength and the environmental and economic impact of using Coltan Mining Waste (CMW) as a substitute for aggregates in concrete and mortar production. To achieve this, the CMW needs to be characterised. The Dreux Gorisse method was primarily used to produce concrete with a strength of 20 MPa at 28 days. The mortars, on the other hand, were formulated according to the NF P 18-452 standard. The environmental impact of using CMW as substitutes for natural aggregates in the production of concrete and mortar was analysed using SimaPro software. The results showed that mortars and concrete made with CMW have comparable compressive strengths to the reference mortar and concrete;reduce the negative impact on ecosystem quality, human health, resources, and climate change. It has also been shown that the substitution of aggregates by CMW reduces the cost of concrete and mortar as a function of the distance from the aggregate footprint.

Mathematical models for properties of mortars with admixtures and recycled fine aggregates from demolished concretes

In order to expand the engineering application of recycle aggregate mortars （RAM） with aggregates from demolished concretes, the models for the properties of RAM and the replacement rate of these recycled fine aggregates were proposed. First, different kinds of mathematical models for the basic properties （compressive strength, water retention rate, and consistency loss） of RAM with two kinds of admixtures, thickening powders （TP） and self-made powdery admixtures （SSCT） designed for RAM, and the replacement rates were established, while the average relative errors and relative standard errors of these models were calculated. Additionally, the models and their error analyses for the curves of drying shrinkage and curing time of RAM ＋ SSCT at different replacement rates were put forward. The results show that polynomial functions should be used to calculate the basic properties of RAM ＋ TP and RAM ＋ SSCT at different replacement rates. In addition, polynonfial functions are the most optimal models for the sharp shrinkage sections in the curves of drying shrinkage-curing time of RAM ＋ SSCT, while exponential functions should be used as the models for the slow shrinkage sections and steady shrinkage sections.

Effect of SiO_(2) Aerogel-cement Mortar Coating on Strength of Self-Compacting Concrete after Simulated Tunnel Fire

In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires,a SiO_(2) aerogel-cement mortar coating was prepared.Based on the HC curve,a self compacting concrete cube specimens coated and uncoated with SiO_(2) aerogel-cement mortar(SiO_(2)-ACM)were heated to simulate tunnel fire for 0.5,1,1.5,2,2.5,3 and 4 h,respectively.The residual compressive strength was tested after the specimens were cooled to room temperature by natural cooling and water cooling.The results show that,the damages of specimens become more serious as fire time goes on,but the residual strength of specimens coated with SiO_(2)-ACM is always higher than that of uncoated with SiO_(2)-ACM.In addition,the residual strength of specimens cooled by water cooling is lower than that of natural cooling.However,for the specimens coated with SiO_(2)-ACM,the adverse effects of water cooling are lessened.With the increase of fire time,the protective effect of SiO_(2)-ACM is still gradually improved.Finally,a formula was established to predict the residual 150 mm cube compressive strength of specimens protected by SiO_(2)-ACM after a simulated tunnel fire.

Experimental study on retarding mortar and its application in prestressed concrete

Based on a large number of orthogonal tests and theoretical analyses, the retarding mortar which meets the requirements of retard-bonded prestressed concrete was prepared. Initial setting time of the retarding mortar may vary from several hours to 15 d at 5 ℃-35 ℃ due to quantities and average curing temperature. And its 28 d compressive strength is above 35 MPa. Thus the influence of quantities on setting time and 28 d compressive strength, and the relationship between setting time and average curing temperature were investigated. The optimum quantities were obtained by studying the interaction of admixtures, and the retarding mechanism was discussed. Based on 52 retard-bonded prestressed strands by manual work from 24 retard-bonded prestressed concrete T-beams, static friction drag, change factor κ and friction factor μ were obtained from the test when retard-bonded prestressed strands were tensioned. Application of the retarding mortar will be vast in practical concrete projects.

Behavior of Corrosion-Repaired Concrete Beams Reinforced by Epoxy Mortar

The performance of concrete beams repaired with epoxy mortar was investigated by constructing twelve beam specimens.All the beam specimens were subjected to a constant current for accelerated corrosion.Six specimens were corroded without subsequent reparation as a control group,and the other six beam specimens were corroded and repaired utilizing epoxy mortar.All specimens were tested to failure.During test process,we focused on the failure pattern of beam specimens,structural cracks,mid-deflections,bearing capacity,and probed into the influence of corrosion degree and repair of epoxy mortar on the performance of beam specimens.It was observed that corrosion-repaired beams in the loading test were in a bending failure pattern.It is obvious that cracking loads and bending stiffness of repaired beams and corrosion-repaired beams were larger than those of unrepaired beams and secondly-corroded beams.When the mass loss of main steel bars was smaller than 10%,the bearing capacity of the repaired beams was similar to that of the unrepaired beams.When the mass loss of main steel bars was larger than 10%,the bearing capacity of the repaired beams increased significantly compared with that of the unrepaired beams.

Thermal Characterization of Concrete and Cement Mortar from Construction Sites and Industrial Production Units in the City of Ouagadougou with a View to Standardization in Energy Certification

The present study allowed to carry out a thermal characterization of concrete and cement mortar. Thermal tests were carried out with the KD2 Pro device, on concrete and mortar samples taken from twenty-six (26) construction sites of office buildings and two (2) industrial production units in the city of Ouagadougou. The tests were carried out on rectangular specimens after four weeks (4) of conservation on the site of construction or production of materials. This study seeks to determine the thermal properties of the materials, in particular the thermal conductivity, the thermal diffusivity and the thermal capacity of the samples, in the real conditions of execution of the buildings and environment. The thermal conductivity varies from 1.413 to 1.965 W/m·K, 0.940 - 1.658 W/m·K and 0.703 - 1.149 W/m·K respectively for concrete, cinder block mortar and plaster mortar. Regarding the other properties, especially the capacity and thermal diffusivity, the values vary respectively, from 1070.59 - 1974.67 kJ/kg·K and (3.74 - 6.70) × 10-7 m2/s for concrete, from 1123.69 - 1586.81 kJ/kg·K and (3.38 - 5.65) × 10-7 m2/s for plaster mortar and 1202.51 - 1736.01 kJ/kg·K and (3.82 - 7.36) × 10-7 m2/s for the mortar of building blocks. The conductivity, capacity and thermal diffusivity of industrial mortar vary from 1.019 - 1.229 W/m·K, 792.18 - 1862.58 J/kg·K and (2.75 - 6.80) × 10-7 m2/s, respectively. Only the correlations made between the thermal properties and the density of the samples of the plaster mortar, give good relations namely R2 = 0.9308 for the thermal conductivity, R2 = 0.7823 for the thermal capacity and R2 = 0.9272 for the thermal diffusivity. This study contributes to the establishment of a thermal regulation in Burkina Faso for the adoption of the West African Economic and Monetary Union (WAEMU) Directive 05 on energy efficiency in buildings.

Flexural behavior of textile reinforced mortar-autoclaved lightweight aerated concrete composite panels

To improve the deficiencies of prefabricated autoclaved lightweight aerated concrete(ALC)panel such as susceptibility to cracking and low load-bearing capacity,a textile-reinforced mortar-autoclaved lightweight aerated concrete(TRM-ALC)composite panel was developed in this study.One group of reference ALC panels and five groups of TRM-ALC panels were fabricated and subjected to four-point flexural tests.TRM was applied on the tensile side of the ALC panels to create TRM-ALC.The variable parameters were the plies of textile(one or two),type of textile(basalt or carbon),and whether the matrix(without textile)was applied on the compression side of panel.The results showed that a bonding only 8-mm-thick TRM layer on the surface of the ALC panel could increase the cracking load by 180%−520%.The flexural capacity of the TRM-ALC panel increased as the number of textile layers increased.Additional reinforcement of the matrix on the compressive side could further enhance the stiffness and ultimate loadbearing capacity of the TRM-ALC panel.Such panels with basalt textile failed in flexural mode,with the rupture of fabric mesh.Those with carbon textile failed in shear mode due to the ultra-high tensile strength of carbon.In addition,analytical models related to the different failure modes were presented to estimate the ultimate load-carrying capacity of the TRM-ALC panels.

Performance of Epoxy-Repaired Corroded Reinforced Concrete Beams

Reinforcement corrosion has a serious impact on the durability and safety of reinforced concrete structures.Six reinforced concrete(RC)beam specimens are constructed.After beam specimens are subjected to accelerated corrosion with the constant current,beam specimens are repaired with epoxy mortar and the flexural test of beams is investigated.Then the behaviors of repaired corroded reinforced concrete beams are evaluated.The experimental results show that cracking and ultimate loads of corroded RC beams are enhanced after being repaired.And the strain distributions measured across sections of beam specimens still obey the assumption of plane section.After being repaired,the number of cracks decreases and the crack spacing increases.

Effect of Modified Supplementary Cementitious Material on Performance of Mortar and Concrete in Marine Environment

This study aims to explore the durability issues regarding chloride ion corrosion of concrete structures, and further investigates the modified supplementary cementitious material (MSCM) which acts as a significant enhancer of performance of mortar and concrete. The composition of MSCM includes mineral slag powder, fly ash and inhibitor. The microstructure, sulfate erosion resistance and electric flux of high-performance concrete are tested with MSCM, and the results show that the pore structure of concrete is improved significantly along with excellent electrochemical performance. It is observed that the substantiality of concrete after being mixed with 18% (mass fraction) MSCM is enhanced effectively. The sulfate resistance coefficient of concrete is found to be greater than 1.2, and the electric flux of concrete is less than 600C. These results have demonstrated that the MSCM possesses an excellent electrochemical performance and a wide applicative prospect in marine environment. © 2017, Shanghai Jiaotong University and Springer-Verlag GmbH Germany.

Influence of Thermally Treated Flue Gas Desulfurization(FGD) Gypsum on Performance of the Slag Powder Concrete

The feasibility of flue gas desulphurization （FGD） as concrete admixture was studied. A combined concrete admixture of the thermally-treated FGD gypsum and slag powder was explored. The FGD gypsum was roasted at 200℃ for 60 min and then mixed with the slag powder to form FGD gypsum-slag powder combined admixture in which the SO3 content was 3.5wt%. Cement was partially and equivalently replaced by slag powder alone or FGD gypsum-slag powder, at concentration of 25wt%, 40wt%, and 50wt%, respectively. The setting times, hydration products, total porosity and pore size distributions of the paste were determined. The compressive strength and drying shrinkage of cement mortar and concrete were also tested. The experimental results show that, in the presence of FGD gypsum, the setting times are much slower than those of pastes in the absence of FGD gypsum. The combination of FGD gypsum and slag powder provides synergistic benefits above that of slag powder alone. The addition of FGD gypsum provides benefit by promoting ettringite formation and forms a compact microstructure, increasing the compressive strength and reduces the drying shrinkage of cement mortar and concrete.

Efficiency of Amino Alcohols as Corrosion Inhibitors in Reinforced Concrete

The objective of this paper is to investigate the behaviour of amino alcohol corrosion inhibitors when they are used in reinforced cement mortars either as admixtures in the cement paste or as coating applications on the surface of the rebars. The reinforced cement mortars were exposed to both partial and full immersion in 3.5 wt% NaCl solution. Electrochemical measurements such as half-cell potential and linear polarization technique, as well as weight loss of the embedded rebars were performed in order to obtain information on the corrosion behaviour of the reinforcing steel in cement mortar. Results demonstrate that the amino alcohol corrosion inhibitors offer protection against rebar corrosion in cement mortars.

Experimental investigation on concrete overlaid with textile reinforced mortar:Influences of mix,temperature,and chemical exposure

Textile reinforced mortar is widely used as an overlay for the repair,rehabilitation,and retrofitting of concrete structures.Recently,textile reinforced concrete has been identified as a suitable lining material for improving the durability of existing concrete structures.In this study,we developed a textile-reinforced mortar mix using river sand and evaluated the different characteristics of the textile-reinforced mortar under various exposure conditions.Studies were carried out in two phases.In the first phase,the pullout strength,temperature resistance,water absorption,and compressive and bending strength values of three different textile-reinforced mortar mixes with a single type of textile reinforcement were investigated.In the second phase,the chemical resistance of the mix that showed the best performance in the abovementioned tests was examined for use as an overlay for a concrete substrate.Investigations were performed on three different thicknesses of the textile reinforced mortar overlaid on concrete specimens that were subjected to acidic and alkaline environments.The flexural responses and degradations of the textile reinforced mortar overlaid specimens were examined by performing bending tests.The experimental findings indicated the feasibility of using textile reinforced mortar as an overlay for durable concrete construction practices.

Numerical modelling of reinforced concrete flexural members strengthened using textile reinforced mortars

Externally bonded(EB)and near-surface mounted(NSM)bonding are two widely adopted and researched strengthening methods for reinforced-concrete structures.EB composite substrates are easy to reach and repair using appropriate surface treatments,whereas NSM techniques can be easily applied to the soffit and concrete member sides.The EB bonded fiber-reinforced polymer(FRP)technique has a significant drawback:combustibility,which calls for external protective agents,and textile reinforced mortar(TRM),a class of EB composites that is noncombustible and provides a similar functionality to any EB FRP-strengthened substrate.This study employs a finite element analysis technique to investigate the failing failure of carbon textile reinforced mortar(CTRM)-strengthened reinforced concrete beams.The principal objective of this numerical study was to develop a finite element model and validate a set of experimental data in existing literature.A set of seven beams was modelled and calibrated to obtain concrete damage plasticity(CDP)parameters.The predicted results,which were in the form of load versus deflection,load versus rebar strain,tensile damage,and compressive damage patterns,were in good agreement with the experimental data.Moreover,a parametric study was conducted to verify the applicability of the numerical model and study various influencing factors such as the concrete strength,internal reinforcement,textile roving spacing,and externally-applied load span.The ultimate load and deflection of the predicted finite element results had a coefficient of variation(COV)of 6.02%and 5.7%,respectively.A strain-based numerical comparison with known methods was then conducted to investigate the debonding mechanism.The developed finite element model can be applied and tailored further to explore similar TRM-strengthened beams undergoing debonding,and the preventive measures can be sought to avoid premature debonding.

Utilization of Concrete Waste Aggregates Using Geopolymer Cement

Reuse of concrete waste, especially in large quantity, can save not only material but also cost for its disposal. This paper presents experiment results on the use of fine and coarse aggregates from concrete waste in geopolymer mortars and concretes. Geopolymeric cement is an inorganic compounds of aluminosilicates synthesized from precursors with high content of silica and alumina activated by alkali silicate solutions. Geopolymer in this experiment was synthesized from fly ash as the precursor and sodium silicate solution as the activator. Hardening of geopolymers was performed by heating the casted paste in an oven at -60~Cfor 3 to 36 hours. Compressive strength of geopolymer pastes and mortars using either fresh or waste fine aggregates were in the range of 19-26 MPa. Hardening time of 3 hours at 60~C followed by leaving the test pieces at room temperature for 7 day before testing results in similar strength to that of mortars cured for 36 hours at 60~C followed by leaving the samples at room temperature for 3 days. It suggests that optimum strength can be achieved by combination of heating time and rest period before testing, i.e the specimens age. Applying mix design with a target strength of 40 MPa, conventional Portland cement concretes using fresh aggregates reached 70% of its target strength at day-7. Compressive strength of geopolymer concretes with waste aggregates was -25 MPa at day-3 while geopolymer concretes with fresh aggregates achieved -39 MPa at day-3. It can be concluded that geopolymer concretes can achieve the target strength in only 3 days. However, the expected reinforcing effect of coarse aggregates in concrete was ineffective if waste coarse aggregates were used as the strength of the concretes did not increase significantly from that of the mortars. On the other hand, waste fine aggregates can be reused for making geopolymer mortars having the same strength as the geopolymer mortars using fresh aggregates.

Workability Tests on Fresh Concrete Formulated with Eco-friendly Admixture

Extra-cellular compounds, secreted by microorganisms into their surroundings, can be integrated in concrete composition as admixtures. These substances are important in biofilm formation and some of them can be used as corrosion inhibitor of concrete reinforcement. This paper deals with products made with biological surface active compounds/agents allowing the development of more eco-friendly concrete. The influence of this environmentally friendly bio admixture on setting time, workability, bending and compressive strengths of various mortar based materials made of CEM I, CEM III and CEM V was studied. Mechanical tests were carried out to highlight the influence of admixture in workability and hardening of samples containing the biological product with ratio in the range of 0-2.5%. It was demonstrated that the presence of the new bio-compound admixture in mortar decreases their compressive strength after 28 days of standard curing, in spite of remaining higher than standard minimal strength. Furthermore, Vicat needle experiments have shown a tendency of this admixture to decrease the setting time. A discussion was finally proposed in order to correlate the setting times and the decrease of the mortar compressive strength, corresponding in fact to a hardening delay. This setting time delay could be linked to a delay of the admixtured mortar to increase its resistance. The slump results highlight the action of bio-admixture as a plasticizer on mortars because it increases their workability for a same water-cement ratio. This effect seems variable according to the added amount.

EFFECT OF RECYCLED CONCRETE AGGREGATE QUALITY ON PROPERTIES OF CONCRETE

The possibility of the use of recycled aggregates from the construction industry in green concrete production is of increasing importance to reduce the negative environmental impact associated with construction and demolition wastes.The objective of this study is to investigate the effect of recycled concrete aggregate(RCA)quality on the properties of hardened concrete properties such as compressive strength,splitting tensile strength,density,water absorption capacity and porosity accessible to water.The RCA used in this study was obtained from the crushing of waste concrete with two different compressive strengths(LRCA obtained from the crushing of waste concrete having compressive strengths below 30 MPa and HRCA obtained from the crushing of waste concrete having compressive strengths above 30 MPa).The natural coarse limestone aggregate was 100%replaced with coarse LRCA and HRCA.As a result of the study,the use of 100%HRCA and%100 LRCA instead of limestone coarse aggregate in the concrete adversely affected its mechanical and physical properties.In addition,HRCA showed better performance in terms of compressive strength,tensile strength,water absorption and porosity compared to the use of LRCA.Furthermore,the percentage of adhered mortar on the surface of LRCA and HRCA was analyzed using a computerized micro tomography device,and it was found that the percentages of attached mortar and aggregates are 61%and 35.5%for LRCA,whilst the attached mortar and aggregate contents for HRCA are 45.9%and 53.7%,respectively.

Influences of Carboxyl Methyl Celluloseon Performances of Mortar

Carboxyl methyl cellulose （CMC） was mixed into mortar to improve the waterretention performance of mortar, the quality of floated coat of aerated concrete became better. The consistency and compression strength of mortar with CMC were studied. The water absorption was studied with the method of filter paper. The micro mechanism was researched with X-ray diffraction and scanning electron microscopy（SEM）. The experimental results show the water-holding performance of mortar with CMC is largely improved and it is better when the mixed amount is about 1.5%; the compression strength had a descending trend with the increase of CMC; CMC reacted with calcium hydroxide（CH） into the deposition of calcium carboxyl methyl cellulose.