Durability of ultra-high performance concrete – A review

Ground-glass pozzolan (G) obtained by grinding the mixed-waste glass to same fineness of cement can act as a supplementary-cementitious material (SCM), given that it is an amorphous and a pozzolanic material. The G showed promising performances in different concrete types such as conventional concrete (CC), high-performance concrete (HPC), and ultra-high performance concrete (UHPC). The current paper reports on the characteristics and performance of G in these concrete types. The use of G provides several advantages (technological, economical, and environmental). It reduces the production cost of concrete and decrease the carbon footprint of a traditional concrete structures. The rheology of fresh concrete can be improved due to the replacement of cement by non-absorptive glass particles. Strength and rigidity improvements in the concrete containing G are due to the fact that glass particles act as inclusions having a very high strength and elastic modulus that have a strengthening effect on the overall hardened matrix.

Influence of nano-silica addition on durability of UHPC

The influence of curing regimes on hydration, microstructure and compressive strength of ultra-high performance concrete: A review

High performance concrete (HPC) and ultra high performance concrete (UHPC) are cement based composites with an optimized gradation of granular constituents and a high percentage of discontinuous internal fibre reinforcement [1].HPC mix does not have coarse aggregate which is formulated using the particle packing design model to optimize the matrix density and minimize voids [2].Thanks to its low water content compared to conventional concrete, HPC presents improved mechanical performance and durability [3], [4], [5].Besides having a high compressive strength which exceeds 50 MPa, current research shows that HPC tensile strength may reach 15 MPa.A higher tensile strength in HPC would lead to higher ductility and to the elimination of reinforcement requirements (i.e., bars, wire, mesh).Therefore, there is more flexibility for using the HPC in a wider range of structural shapes and forms [6], [7].Despite of high mechanical performance of this type of concrete, there are some barriers to manufacture HPC: high cost of materials, environmental impact, complex fabrication and curing processes [8], [9].For this reason, it is important to understand the production process.This research analyses the manufacture of HPC and its tensile strength through conventional economic methods.In this study, 5 different HPC mixture designs were considered and 20 cylinders (100 mm x 200 mm) were built for each one to examine the relationship between tensile strength, water to cement ratio, and packing density of the matrix.The material used were: general purpose Portland cement Type I (ASTM C1157/C1157M-20), quartz sand with a diameter of 300 m, and spherical steel particles with a diameter of 2.36 mm.A high range water reducer was also added.Compression and splitting tensile tests were performed according to ASTM C39 and ASTM C496.Among the different HPC mixtures proposed, a split tensile strength at 28 days of 5-15 MPa was measured: a value larger than that observed in Shotcrete type concretes, conventional concretes, and HPC found in the literature.By using undersized aggregates, the packing density of the matrix was optimized.Using a general purpose Portland cement Type I significantly reduces HPC production costs.Additionally, the high range water reducer improves the workability of the mixture.In this research, HPC with high tensile strength was manufactured with common materials and using production methods and tools employed in the fabrication of conventional concretes.The HPC studied here does not require special high temperature curing regimes, high intensity mixers or temperature controlled environmental chambers, as required for currently marketed HPCs.It is possible to scale up the fabrication of the optimized HPC mixture proposed in this study for in-situ applications.

Effect of chloride ion migration behaviour on the microstructure and mechanical properties of ultra-high performance concrete: A review

Microstructure and radiation shielding characteristics of PVA fiber-reinforced ultra-high performance concrete

The objective of this study is to investigate the effects of using local waste materials on the properties of fresh and hardened high performance and self-compacting concrete. Crushed ceramic products and steel slag from electric-arc furnaces were used as partial replacements of traditional concrete raw materials in the production of self-compacting and high performance concrete, which were obtained from local factories in Kuwait. Preliminary results have shown that using crushed ceramic products (in the form of powder and 3/8” aggregates) increases the rate of strength gain as the concrete cures, while using electric-arc furnace slag increases the compressive strength of the benchmark concrete mix by up to 40%.

The objective of this study is to investigate the effects of using local waste materials on the properties of fresh and hardened high performance and self-compacting concrete. Crushed ceramic products and steel slag from electric-arc furnaces were used as partial replacements of traditional concrete raw materials in the production of self-compacting and high-performance concrete, which were obtained from local factories in Kuwait. Results have shown that using crushed ceramic products (in the form of powder and 3/8” aggregates) increases the rate of strength gain as the concrete cures, while using electric-arc furnace slag increases the compressive strength of the benchmark concrete mix.

Considering its superior engineering properties, ultrahigh performance concrete (UHPC) has emerged as a strong contender to replace normal strength concrete (NSC) in diverse construction applications. While the mechanical properties of UHPC have been thoroughly explored, there is still dearth of studies that quantify the durability of UHPC, especially for sustainable mixtures made with local materials. Therefore, this research aims at investigating the alkali-silica reactivity (ASR) potential in sustainable UHPC in comparison with that of NSC. Sustainable UHPC mixtures were prepared using waste untreated coal ash (CA), raw slag (RS), and locally produced steel fibers. UHPC and benchmark NSC specimens were cast for assessing the compressive strength, flexural strength, and ASR expansion. Specimens were exposed to two curing regimes: accelerated ASR conditions (as per ASTM C1260) and normal water curing. UHPC specimens incorporating RS achieved higher compressive and flexural strengths in comparison with that of identical UHPC specimens made with CA. ASR expansion of control NSC specimens exceeded the ASTM C1260 limits (>0.20% at 28 days). Conversely, experimental results demonstrate that UHPC specimens incurred much less ASR expansion, well below the ASTM C1260 limits. Moreover, UHPC specimens incorporating steel fibers exhibited lower expansion compared to that of companion UHPC specimens without fibers. It was also observed that the mechanical properties of NSC specimens suffered more drastic degradation under accelerated ASR exposure compared to UHPC specimens. Interestingly, UHPC specimens exposed to accelerated ASR conditions attained higher mechanical properties compared to that of reference identical specimens cured in normal water. Therefore, it can be concluded that ASR exposure had insignificant effect on sustainable UHPC incorporating CA and RS, especially for specimens incorporating fibers. Results indicate that UHPC is a robust competitor to NSC for the construction of mega-scale projects where exposure to ASR conducive conditions prevails.

Bonded concrete overlays are frequently used to rehabilitate concrete bridges. This necessitates that the overlay material develops high bond to the substrate, high cracking resistance,and adequate durability. Typical thicknesses of bonded bridge overlays prepared with conventional concrete (CC) can vary between 50 and 125 mm. However, CC overlays can exhibit limited service life and can significantly increase dead load on the bridge structure. Ultra-high performance concrete (UHPC) is regarded as a promising for use in thin UHPC overlays of 25 to 50 mm. Such novel material can extend the service life of bridge decks and minimize additional dead load. However, UHPC is prone to high autogenous shrinkage and restrained shrinkage from the substrate, which can lead to cracking and delamination of the overlay material. Shrinkage mitigation strategies include the use of pre-saturated lightweight sand (LWS) for internal curing and CaO-based expansive agent (EXC). The LWS was used at 60% volume replacement of the rivers and in the investigated UHPC; the UHPC was proportioned with 70% river sand and 30% masonry sand, by volume. The EXC was used at 0, 5%, and 10%, by mass of binder. The UHPC was prepared with 0.2w/b and 20% and 25% fly ash and silica fume replacements, respectively. Figure1shows the effectiveness of LWS and EXC on total shrinkage, which is considered as the autogenous shrinkage at one day plus the drying shrinkage after 7 days of moist curing. The use of 60% LWS led to approximately 50% enhancement in compressive strength compared to the reference mixture made without any LWS and EXC. However, the incorporation of EXC in UHPC with LWS reduced strength given the reduction in water available for cement hydration, which was consumed by the hydration the CaO. Four UHPC mixtures made with EXC and LWS as well as CC overlay mixture were used to cast thin overlays of 25, 38, and 50 mm onto substrate specimens measuring 2×1×0.15m. The CC substrate was cast 6 months before the overlay placement. Strain gauges, relative humidity sensors,and thermocouples were installed at various locations at the bottom of the overlay materials near the interface with the substrate. In the initial six months,the slab specimens were kept indoor and were then moved outdoors (Rolla, MO). The variations in temperature are shown in Fig.2. Figure3showsthe variations of strain determined at edge locations of the composite slabs for samples cast with 38-mm thick overlays. The strain in the reference UHPC was approximately±100 m/m. The incorporation of 60% LWS resulted in approximately strain 0 to 200 μm/m. Furthermore, the addition of 5% and 10% EXC along with 60% LWS led to strain approximate values of 100 to 300 and 500 to 700 μm/m, respectively, thus indicating that the overlay material was always in compression. Pull-out tests were conducted after approximately 185, 350, and 500days.As shown in Fig. 4,the failure for the CC overlay specimens occurred at the interface, whereas that for UHPC specimens was in the substrate. The bond of the latter system varied between approximately 2 and 2.8 MPa compared to 1.5 MPa for the CC overlay. Similar observation was noted for the 25-and 50-mm thick UHPC overlays. Further work is underway to compare bond strength between the various UHPC mixtures with the CC substrate using specially designed test specimens.

The effect of clay as nanomaterial or nanoclay (NC) on corrosion potential of steel reinforcement embedded in ultra-high performance concrete (UHPC) due to the early age properties of UHPC was investigated. In this present research, ordinary Portland cement (OPC) was partially replaced by NC at 1, 3, and 5 % by weight of cement to produce the nanoclayed UHPC. It is well recognized that the corrosion of steel reinforcement would affect the service life of the reinforced concrete structure performance. To overcome this problem, UHPC was benefited due to its superior characteristic in term of density and durability as compared to OPC concrete itself. In this present research, half-cell potential (HCP) was used to monitor and measure the corrosion potential of steel reinforcement embedded in UHPC and nanoclayed UHPC. Meanwhile, weight loss of corroded steel reinforcement and pH values of hardened UHPC and nanoclayed UHPC were also conducted as follows to the specific procedures. All the samples were immersed in 3 % sodium chloride solution up to 91 days of exposure. The results revealed that the corrosion activity of steel reinforcement embedded in UHPC with 5 % NC recorded the lowest corrosion potential readings compare to those UHPC. It is also shows that the pH value of concrete and weight loss of corroded steel reinforcement in UHPC alone is highest compared to UHPC incorporating different levels of NC. As regards to the results, it is revealed that replacing NC as a replacement to cement significantly enhanced the chloride penetration of nanoclayed UHPC. It is also indicated that the corrosion potential decreased with the increase of NC and as a result delayed the corrosion initiation.

Demonstration on the coalescence of fiber reinforced concrete with self-compacting concrete

The low water/binder ratio of ultra-high performance concrete (UHPC) often results in its high autogenous shrinkage. Our study explored the effect of the single or binary addition of a CaO-based expansive agent (CEA) and steel fibers on flowability, compressive strength, flexural strength, microstructure, and autogenous shrinkage of UHPC. X-ray diffraction (XRD), thermogravimetric (TG) analysis, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were applied to reveal the effects of CEA and steel fibers on hydration products and microstructure characteristics of UHPC. Experimental results show that the autogenous shrinkage of UHPC decreased markedly with the single or binary addition of CEA and steel fibers. Relative to the control group, autogenous shrinkage of UHPC with 2.5% dosage of single steel fibers, 6% dosage of single CEA, and binary addition of 2.5% steel fibers and 6% CEA decreased 17.8%, 10.9%, and 30.8% at 180 days, respectively. Steel fibers could enhance the mechanical performance of UHPC; nevertheless, they would decrease the flowability of UHPC. Meanwhile, the addition of CEA in the UHPC mixture not only maintained the mechanical properties and flowability but also decreased the autogenous shrinkage. Diffraction peak intensity and endothermic peak of Ca(OH)2 and the pore volume of 10–50 nm diminished with the content of CEA; however, that of C-S-H gel and ettringite increased. The prediction accuracy of nine shrinkage models (FHWA model, Lee model, Yoo model, JSCE model, B4 model, JonassonH model, Eurocode 2 model, CEB model, and DilgerW model) is analyzed with RE, Rnew2, and autogenous shrinkage of UHPC in this paper.

Ultra High-Performance Concrete (UHPC) is a cement-based composite material with great strength and durability. Fibers can effectively increase the ductility, strength, and fracture energy of UHPC. This work describes the impacts of individual or hybrid doping of basalt fiber (BF) and steel fiber (SF) on the mechanical properties and microstructure of UHPC. We found that under individual doping, the effect of BF on fluidity was stronger than that of SF. Moreover, the compressive, flexural, and splitting tensile strength of UHPC first increased and then decreased with increasing BF dosage. The optimal dosage of BF was 1%. At a low content of fiber, UHPC reinforced by BF demonstrated greater flexural strength than that reinforced by SF. SF significantly improved the toughness of UHPC. However, a high SF dosage did not increase the strength of UHPC and reduced the splitting tensile strength. Secondly, under hybrid doping, BF was partially substituted for SF to improve the mechanical properties of hybrid fiber UHPC. Consequently, when the BF replacement rate increased, the compressive strength of UHPC gradually decreased; on the other hand, there was an initial increase in the fracture energy, splitting tensile strength, and flexural strength. The ideal mixture was 0.5% BF + 1.5% SF. The fluidity of UHPC with 1.5% BF + 0.5% SF became the lowest with a constant total volume of 2%. The microstructure of hydration products in the hybrid fiber UHPC became denser, whereas the interface of the fiber matrix improved.

A sufficient resistance of concrete structures to fire was always taken for granted. The concrete’s low thermal conductivity ensures an overall good thermal protection of the concrete’s reinforcement, even during longer fire impact. In contrast to ordinary performance concrete used in most structures, the behavior of high (HPC) and ultra-high performance concrete (UHPC) at high temperatures exhibits an increased tendency to explosive spalling and must be considered as critical. Explosive spalling might occur at high temperatures, leading to a direct fire exposure onto the reinforcement steel and a reduction of the cross section. The risk of explosive spalling of HPC and UHPC can be reduced with a modified concrete mixture including polypropylene fibers (PP-fibers); however, temperature-related damage cannot be excluded in general. Another possibility is the use of fire protective concrete linings, acting as a thermal barrier or narrow spaced stirrups. However, their application is still difficult due to the lack of existing design criteria. Within the framework of a research project at the Institute of Structural Engineering (IBK) at ETH Zurich, several tests on the analysis of the risk of temperature-related explosive spalling of HPC and UHPC was carried out. In this report, the explosive spalling of unprotected concrete cylinders (o = 150 mm, h = 300 mm) was investigated using linear heating. Chapter 2 describes these tests. In chapter 3, the behavior of HPC and UHPC containing PP-fibers was analyzed. Different amounts of PP-fibers with varying fiber geometry were tested with the same base concrete mixture. The influence of the PP-fiber’s geometry on the intensity of explosive spalling was clearly indicated. Tests on the porosity and permeability of concrete after cooling from high temperatures are described in chapters 4 and 5. Small concrete fragments (l = 4 mm) were used to determine the cumulative pore volume using mercury intrusion porosimetry. Concrete before and after explosive spalling was analyzed, as well as the influence of PP-fibers on the porosity at different temperature levels. Tests on permeability are described in chapter 5. The gas permeability was analyzed for concrete discs (o = 150 mm, h = 40 mm) at room temperature, after cooling from high temperatures of up to T = 500°C. The influence of steel and PPfibers on the concrete’s permeability was studied in these tests. Chapter 6 deals with the use of protective linings on concrete structures. The required material properties as input material properties for modeling and dimensioning of the linings were determined experimentally and analyzed. A description of tests on UHPC slabs (l • w • h = 1100 • 900 • 150 mm3) protected either with PP-fibers or protective lining is presented in the last part of this report (chapter 7). These slabs were heated according to the standardized ISO-fire curve [1] for a period of t = 120 min. The present test report describes the test set-up for all experimental investigations and summarizes the results. Further analysis or design models will be given in a research publication.