•Hydrologic and mechanical properties of pervious concrete were studied.•The optimal aggregate type from the hydrologic point of view is diabase.•An aggregate of sharp grain edges allows the water to ...pass smoothly through the pore system.•A coarser aggregate fraction results in better hydraulic and mechanical properties.
Six mixtures of single-sized pervious concrete were prepared with three different types of aggregates (dolomite, diabase, and steel slag from a Croatian landfill near the town of Sisak) and with two different aggregate fractions (4–8 mm and 8–16 mm). Each pervious concrete mixture contained 10% of sand from the Drava River. The hydrologic properties of the pervious concrete mixtures are compared in order to define the aggregate type that will ensure the best drainage properties. The draining capability was tested by three methods: the constant head and falling head methods on the small samples, and the standard test method for testing the infiltration rate of in-place pervious concrete by ASTM C 1701-09. The possibility of pervious concrete application as a surface layer in pavement construction in the European area is estimated according to the achieved mechanical properties. The optimal aggregate type for preparing pervious concrete from the hydrologic point of view is diabase because of its sharp grain edges, which allow the water to pass smoothly through the pore system. None of the studied mixtures satisfied the set criteria on the mechanical properties of concrete for the surface layer of pavements in the European area. However, it is observed that the coarser aggregate fraction will result in better hydraulic and mechanical properties of pervious concrete.
•The use of hemp fibers for improving fire resistance of concrete has been studied.•The concrete specimens were heated to 400 °C and cooled.•Fibers did not significantly influence the residual ...properties concrete.•Visual observations showed that the hemp fibers were partially disintegrated.•The incompletely disintegrated hemp fibers could reduce crack propagation.
This study investigated the use of hemp fibers for improving the fire resistance of concrete. The characterization of the fibers was carried out through SEM, TGA/DSC, FTIR and crystallinity index. A reference concrete mixture, polypropylene fibers mixture, and four mixtures with different chemically treated hemp fibers were prepared. The concrete specimens were heated to 400 °C and cooled. Their compressive strength, static modulus of elasticity, residual weight, and residual ultrasonic pulse velocity were then determined and compared. The addition of fibers did not significantly influence the fire resistance of the concrete in terms of the residual properties. Visual observations from scanning electron microscope and microimages of the concrete mixtures showed that the hemp fibers were partially disintegrated within the concrete after being heated; thus, the incompletely disintegrated hemp fibers could reduce crack propagation at high temperatures thus improving the fire resistance of concrete.
In this paper, the resistance to the freeze/thaw cycles for four groups of mortars (lime—LM, lime based—LBM, cement—CM, and aerated cement—ACM mortars) with different amount of mortar components ...within each group is quantified via a ratio of flexural/compressive strength after and before exposure to freeze/thaw cycles. Using a pore system obtained by three different methods (mercury intrusion porosimetry, X-ray micro-computed tomography analysis, and SEM (Scanning Electron Microscopy) analysis), an attempt was made to explain why some mortars achieved better resistance to freeze/thaw cycles than others. The mortars with lime as a binder in the composition (LM and LBM groups) did not survive the freezing and thawing regime, while no visible damage was recorded in samples of the CM and ACM group. It is concluded that the low initial value of the mechanical properties of the LM and LBM mortars, as well as the higher proportion of harmful pores (pores greater than 0.064 μm) compared to CM and ACM mortars are responsible for their poor durability. According the results of nanotomography, it is concluded that the most important factor influencing freeze/thaw resistance is pore connectivity—the higher the connectivity of the macropores, the higher the freeze/thaw resistance of the mortar. SEM analysis proved to be a very useful method for aerated cement mortars as it revealed the pore sizes that were not covered by mercury porosimetry and nanotomography.
The causes of cracks in concrete are varied, and regardless of their origin, these cracks invariably have a detrimental impact on the durability of concrete structures and escalate their maintenance ...costs. This paper presents a comprehensive review of current knowledge regarding the methods of self-healing in concrete, ranging from autogenic and improved autogenic self-healing to the autonomous self-healing of concrete. Particular emphasis is placed on the methods of autonomous concrete self-healing: the bacterial healing method, the crystalline hydrophilic additives healing method, and the capsule-based self-healing method. The hypothesis is that applying these self-healing methods could potentially prevent damages or cracks in concrete caused by freeze-thaw cycles, thereby extending the lifespan of concrete structures. The mechanism of action and current achievements in the field are provided for each method.
This study examines the influence of raw material characteristics, methods of shaping and of parameters of firing process of clay bricks, on pore-size distribution and on resistance to freeze-thaw ...cycles (with particular emphasis on the retention time of the specimens at the maximum achieved temperature). Pore-size distribution was measured by mercury-intrusion porosimetry, while the resistance to freeze-thaw cycles was assessed by exposing the bricks to freeze-thaw cycles (HRN B.D8.011 standard) monitoring the appearance of surface changes, decrease of compressive strength as well as the Maage factor. A correlation was set up between the Maage factor and the ratio of the compressive strength before and after freezing as a quantitative indicator of bricks resistance to frost. By using this correlation for all the examined bricks, regardless of their raw material and shaping procedure, a low coefficient of correlation (R
= 0.26) was obtained. When processed separately, machine-made bricks had a significantly higher correlation coefficient value (R
= 0.60) than the hand-made bricks (R
= 0.28).
This paper estimates the frost resistance of bricks using the ratio of compressive strength before freezing to compressive strength after freezing to describe the damage degree of bricks being ...exposed to freeze-thaw cycles. In an effort to find the ratio that clearly distinguishes resistant bricks from non-resistant bricks, the authors attempted to establish the correlation between the ratio and Maage factor as a recognized model for assessing brick resistance. To clarify the degree of damage of individual bricks, the pore size distribution has been investigated by means of mercury porosimetry. Additionally, micro computed X-ray tomography (micro-CT) has been employed to define the influence of the type of pores (open or closed) and their connectivity on the frost resistance of bricks. According to the results, it can be concluded that there is a good correlation between the Maage factor and the ratio of pre- to post-freeze-thaw cycle compressive strengths, and that the latter ratio strongly correlates with the percentage of large pores (≥3 mm) in the brick. If such a correlation could be confirmed in a larger sample, then the ratio of pre- to post-freeze-thaw cycle compressive strengths could be used as a new method for assessing brick resistance to freeze-thaw cycles and it would be possible to determine the minimum percentage of large pores required to ensure the overall resistance of brick to freeze-thaw conditions. The complexity of the problem is, however, evidenced by the fact that no clear connection between the type (open versus closed) or connectivity of pores and the frost resistance of bricks could be revealed by micro-CT.
Agricultural biomass ash is a waste material produced by incineration of residue from fields after harvesting crops. The use of agricultural biomass in industry produces large quantities of ash that ...represent an ecological problem. Another ecological problem is the dependency of road building on natural materials, which has been traditionally used for all pavement layers. Today, roads are built on less accessible and suitable terrains, increasing the need for improving the mechanical characteristics of locally available materials by various means of stabilisation. Within this research, three agricultural biomass fly ashes are used as lime substitutes for hydraulically stabilised soil. The purpose of this research is evaluation of potential use of agricultural biomass fly ash for the soil stabilisation of road works, i.e., for embankment and subgrade purposes. The results indicate that there is a potential of using barley, sunflower seed shells and wheat fly ash as lime substitutes in the soil stabilisation of road works. The strength characteristics of stabilised soil incorporating biomass fly ash are highly dependent on its chemical composition. Using a three-dimensional digital image correlation technique, it is concluded that the elastic properties of stabilised soil correlate to a fracture mechanism that can be efficiently defined by this modern research tool.
This paper presents an experimental investigation of the compressive behavior of high-strength self-compacting concrete exposed to temperatures up to 600 °C. Ten different concrete compositions were ...tested, in which part of the cement (by weight) was replaced by three different mineral additives (5-15% metakaolin, 20-40% fly ash and 5-15% limestone). The stress-strain curves, compressive strength, modulus of elasticity and strain at peak stress were evaluated from uniaxial compression tests. Scanning electron microscope micrographs were also taken to evaluate the damage caused by the high temperatures. A sharp decrease in mechanical properties and an increase in peak strain were observed already after 200 °C for all mixes tested. The different mineral additives used in this study affected the variations of residual compressive strength by 24% and peak strain by 38%, while the variations of residual modulus elasticity were 14%. Comparing the obtained results with the recommendations for compressive strength given in regulatory code EN 1992-1-2 for high strength concrete, it can be concluded that the strength loss observed in EN 1992-1-2 at temperatures up to 400 °C is too conservative. The Popovics model for the relationship between stress and strain provided a good approximation for the experimentally determined stress-strain curves at different temperatures.
This paper aims to assess the influence of clogging on paving material (pervious concrete) drainage characteristics as well as the influence of the properties of an unbound base layer on drainage ...characteristics of the whole paving system. The clogging influence has been studied measuring the drainage characteristics on pervious concrete flags before and after their clogging, according to ASTM C1701-09. Additionally, the drainage characteristics of uncontaminated pervious concrete as a paving material was assessed using the falling head method. To assess the influence of properties of an unbound base course (UBC) on drainage characteristics of the whole paving system, the unbound base layer was compacted in two different levels of compaction and the drainage characteristics were measured (according to ASTM C1701-09). It is concluded that pervious concrete prepared with a smaller aggregate fraction is more prone to clogging. Regarding the influence of UBC, it is important to find a balance between pervious concrete infiltration and UBC exfiltration rate, particularly in a case of pervious concrete flags made of coarse aggregate.
This paper investigates the effectiveness of a specific crystalline waterproofing admixture (CWA) in concrete as a function of a water-binder ratio. Four concrete mixes with and without CWA were ...prepared; two of them with a water-binder ratio of 0.45 and two of them with a water-binder ratio of 0.55. Water permeability and compressive strength were tested on hardened concrete specimens and self-healing of cracks over time was observed. Cement paste and CWA paste were prepared to clarify the results obtained on the concrete specimens. SEM and EDS and XRD and FTIR were performed on the hardened pastes to explain the mechanism of CWA working. The results show that the addition of CWA had no significant effect on the compressive strength of the concrete, but reduced the water penetration depth in the concrete, and the reduction was more effective for mixes with lower water-binder ratio. Regarding the self-healing effect, it can be concluded that the addition of CWA improves the crack healing in concrete, but the efficiency of self-healing is highly dependent on the initial crack width. The mechanisms involved in the reduction of water penetration depth and crack healing in concrete can be explained by different mechanisms; one is creation of the CSH gel from unreacted clinker grains, then formation carbonate, and additional mechanism is gel formation (highly expansive Mg-rich hydro-carbonate) from magnesium based additives. The presence of sodium silicate, which would transform into carbonate/bicarbonate, also cannot be excluded.
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