Mortar beams incorporating carbon nanofibers (CNFs), which were synthesized in situ on Portland cement particles, were used to produce nanomodified Portland cement sensors (SmartCem sensors). SmartCem sensors exhibited an electrical response comparable to a thermistor with a temperature coefficient of resistivity of − 0.0152/ °C. The highest temperature sensing was obtained for the SmartCem sensor, which contained ~ 0.271 wt.% of CNFs. The calculated temperature sensitivity was approximately 11.76% higher in comparison with the mortar beam containing only unmodified Portland cement. SmartCem sensors were used to monitor the cement hydration in large-scale self-compacting concrete beams. The measurements were conducted after casting for 7 days. Additionally, commercially available thermocouple and humidity sensors were used as references. The results showed that changes in electrical resistivity measured by the SmartCem sensor were well aligned with the ongoing hydration processes.

Results are presented from a RILEM Round Robin Investigation on tests and analyses of anchor bolts in concrete. About 60 researchers have performed more than 180 tests and 200 analyses in America, Asia, Australia and Europe. The investigation shows that it is possible to reasonably correctly analyse both plane and axi-symmetric anchor bolt problems. However, there are difficulties to overcome and correct boundary conditions are important both in analyses and tests.

Results are presented from a RILEM Round Robin Investigation. It deals with tension stiffening of reinforcement bars embedded in concrete tie elements. Seven groups of researchers have performed some 50 tests and analyses. Parameters discussed are: cover thickness, crack spacing, bar size, tension stiffening of naked reinforcing bars, and influence of concrete strain softening.

Mortar and concrete can be divided into two phases of solids and water where water fills the voids between the grains and also coats the surface of particles. The current study investigates the influence of the thickness of coating water on flow spread of mortars and concretes. The article aims at correlating consistency of concretes to consistency of mortars. It was found that the flow behavior of granular mixtures can be directly related to the average water film thickness that envelops the particles. The concept was tested on mortar and concrete mixtures with different cement types, aggregate grading, aggregate shape, fineness and proportioning; proving water film thickness to be the most critical parameter affecting the flow. The results of the study indicate the possibility of predicting the flowability of mixtures by knowing the enveloping water film thickness. In addition, the relation between flowability of mixtures measured in different sizes of slump cone is explored to enable translating flow of mortars measured in mini-slump cone to flow of concrete obtained from Abram’s cone.

In order to stabilize light-frame timber buildings against horizontal loads, the diaphragm or in-plane action of roofs, floors and walls is often used. This paper deals with the influence of imperfections such as gaps and uplift on the horizontal displacement of fully anchored shear walls. The significance of analyzing the effects of imperfections is evident when evaluating the stiffness of shear walls; tests of walls show that the horizontal displacement is underestimated in calculations using the stiffness of sheathing-to-framing joints as obtained from experiments. Also, in real structures where hold-downs are used according to the elastic design method, the influence of gaps and uplift should be included in order to obtain realistic displacements in the serviceability limit state. A new elastic model for the analysis, based on linear elastic behaviour of the mechanical sheathing-to-framing joints, is presented and the equations for the stiffness and the deflection versus the number of segments in the wall are derived. The fully anchored condition for the shear walls are modelled by applying a diagonal load to the wall. Three types of imperfections are evaluated: gaps at all studs, a gap only at the trailing stud, and gaps at all studs, except at the trailing stud. It is shown that the effect of imperfections on the stiffness of the wall in the initial stage is considerable. Depending on the distribution of the gaps and the number of segments included in the shear wall, the displacement of the shear wall is increased several times compared to that of a fully anchored shear wall with no gaps; e.g. for a single segment wall more than three times. However, for walls with more than six to ten segments, the effect of imperfections can be neglected. Finally, the theoretical model is experimentally verified.

This paper relates the second part of the investigation of air-cooling in concrete; the first part is presented in `Air cooling of concrete by means of embedded cooling pipes Part I: Laboratory tests and heat transfer coefficients'. Embedded cooling pipes are used to reduce the risk of thermal cracking in early age concrete. Traditionally, water has been used as a cooling medium, but air cooling has been shown to be advantageous for many applications. The experimentally-determined heat transfer coefficients of cooling pipes, have been used and verified in comparisons of in situ measurements at the Igelsta Bridge in Sodertalje, Sweden. The close agreement between measured and calculated temperatures of air-cooled sections seems to justify the use of the averaged heat transfer coefficients determined in [1]. Some exemplifying calculations are also shown, and the general behaviour of cooled structures is discussed. The principles of designing a cooling system for a general case are proposed. It is concluded that it is possible to design prismatic structures, such as a columns, by the use of existing models and measured heat transfer coefficients

Embedded cooling pipes can be used to reduce the temperature rise in massive structures as a measure against thermal cracking. When air is used as a cooling medium, relatively large diameters with profiles causing friction losses along the pipe are preferred. In this paper, heat transfer coefficients for two different types of cooling pipes have been determined for different pipe flows in combination with various temperature levels. This paper relates to the first part of the investigation dealing with the laboratory tests of heat transfer coefficients. The second part, dealing with application in design, is presented in "Air cooling of concrete by means of embedded cooling pipes-Part II: Applications in design"

Glulam members often become large in cross section where heavy loads should be carried. In some applications this may cause problems if limitations on height are posed. A possible solution is to reinforce the member by e.g. bonding fibre reinforced polymer (FRP) on the beams or between the glulam lamellas. The aim of this paper is to investigate the possibility of strengthening glulam beams by the use of pultruded rectangular carbon fibre rods and to establish the anchoring length for this system. Tests were performed in three different series completed by a reference series, 10 specimens altogether. All tests were performed as short-term experiments in four-point bending. The experimental results were compared to analytical models in several aspects. The overall capacity of the beam was established using an analogy with concrete beams. Special attention was made to establishing the anchoring length of the reinforcement bar, since this is governing to avoid premature failures. The anchorage length was tested and an analytical model established. The agreement between the analytical critical anchoring length and the test result was satisfactory. The proposed reinforcement method increased the short-term flexural load-carrying capacity by 49-63% on average.

Timber joints can experience ductile failures as modeled by Johansen in the European Yield Model adapted in Eurocode 5, or they can fail in a brittle manner. In nailed or screwed joints where the fastener does not protrude through the timber, plug shear failure can occur where an entire plug defined by the perimeter of the joint is torn away from the timber. The brittle plug shear failure, which can occur in joints loaded in tension parallel to the grain, results in a lower joint resistance than the ductile failure modes. The aim of this study is to evaluate existing prediction formulas for plug shear failure in timber connections, compare them to test results and observations, and propose a new prediction formula. Test results from four different experimental studies are presented. Using hypothesis testing, a prediction formula for plug shear failure is proposed based on 92 experiments. The resistance of the tensile failure mode of plug shear failure is best modelled by the tensile resistance of the end face of the plug. The resistance of the shear failure mode of plug shear failure is best modelled by the shear resistance of the bottom area of the plug taking into account the volume effect on shear strength. The model currently in Annex A of Eurocode 5 is overestimating the plug shear resistance compared to the test results analysed in this research. To avoid plug shear failure, short and wide joints are preferred, minimising the number of fasteners in line with the load and grain direction

In order to stabilize light-framed timber buildings against lateral loads, the diaphragm action of roofs, floors and walls is often used. This paper deals with an elastic analysis model for fully anchored sheathed wood frame shear walls. The model is based on the assumption of a linear elastic load-slip relation for the sheathing-to-framing joints. Only static loads are considered. The basic structural behaviour and assumptions for the elastic model are elucidated. Formulas for the load-bearing capacity and the deformation of the shear walls in the ultimate and serviceability limit states, respectively, are derived. Both a discrete point description and a continuous flow per unit length modelling of the fasteners are discussed. Also, the forces and displacements of the fasteners and sheathing are derived. The effect of different patterns and spacing of the fasteners on the capacity and displacement of the wall is illustrated. The influence of flexible framing members and shear deformations in the sheets, and also the effect of vertical loads on the shear wall, both with respect to tilting and second order effects, on the horizontal load-bearing capacity and displacement are evaluated. The stress distribution and the reaction forces at the ends of the different framing members are derived. The elastic model is experimentally verified and an illustrative example is given.

Early-age frost damage to concrete used in winter construction or in cold environments negatively affects the development of the hydration process and the performance of the concrete, thereby reducing the service life of the building structure. Experimental research was carried out to investigate the compressive strength, resistance to chloride penetration and resistance to freeze–thaw of concrete specimens subjected to early-age freeze–thaw cycles (E-FTCs). The effects that different pre-curing times of concrete and mineral admixtures have on the properties of early-age frost-affected concrete were also analyzed. Results show that the earlier the freeze–thaw cycles (FTCs), the poorer the later-age performance. Later-age water-curing cannot completely restore the damage that E-FTCs do to concrete. In the same conditions used in this study, the effects of E-FTCs on later-age mechanical and durability properties of ordinary Portland cement concrete (OPC) are small. The incorporation of fly ash significantly reduces the resistance to freeze–thaw of concrete during early-age and later-age. The presence of silica fumes has an adverse effect on the later-age resistance to freeze–thaw. In general, the recovery percentage of later-age durability indexes of concrete subjected to E-FTCs is lower than that of compressive strength. For concrete subjected to E-FTCs, it is more important to ensure the recovery of later-age durability.

Timber-concrete composite beams and slabs require interlayer connectors, which provide composite action in the cross-section. A range of mechanical connectors is available on the market with an extensive variety of stiffness and strength properties, which are fundamental design parameters for the composite structure. Another crucial parameter is the cost of the connector, including the labour cost, that if too high may prevent the use of the composite system. In order to reduce the construction cost and make timber-concrete structures more widespread on the market, it is believed that a high degree of prefabrication should be achieved. For a simple and cost effective construction process, the use of "dry" connections, which do not require the pouring and curing of concrete on site, may represent a possible solution. This paper reports the outcomes of an experimental programme aimed to investigate a number of different mechanical "dry-dry" connectors previously embedded into a prefabricated concrete slab. Direct shear tests on small blocks made of a glulam segment connected with a prefabricated concrete slab were performed. The shear force-relative slip relationships were measured and all the relevant mechanical properties such as slip moduli and shear strengths were calculated. It was found that some of the new developed connection systems for prefabricated concrete slab can perform as satisfactorily as those for cast-in-situ slabs, with the additional benefit of being relatively inexpensive.

The purpose of this investigation has been to evaluate the effect of quartz filler on concrete strength and microstructure, and to see if it is possible to replace cement with filler without loss of strength. Fillers are materials whose function in concrete is based mainly on size and shape. They can interact with cement in several ways; to improve particle packing and give the fresh concrete other properties, and even to reduce the amount of cement in concrete without loss of strength. Quartz was chosen as filler material, since it is inert and is available both as a by-product and a natural raw material. Different amounts of filler were used in the various experiments, as well as different particle size distributions. The results are positive: fillers can partially replace cement and at the same time improve the properties and the microstructure of the concrete. This research is part of a larger project that aims to find uses for by-products in concrete.

The splitting of concrete covers due to the expansive action of corrosion has been investigated by a finite element method (FEM) based on an element-embedded crack concept called the inner softening band. Fictive cross-sections, with and without transverse reinforcement, were studied. The concrete composition (plain and fibrous high-strength concrete) and the cover thickness were varied. The model produced credible fracturing behaviour in concrete covers and explained the mechanical origin of the cracks. For cover thicknesses less than two times the bar diameter, fibres do not seem to have any significant effect on occurrence of splitting cracks. However, fibres are effective to arrest the opening of arisen splitting cracks and to redistribute the strains to other cracks. Hence, fibres may postpone or prevent a total spalling of concrete covers. A larger cover is necessary not only to prolong the initiation period, but also for the fibres (2 volume-%) to be effective beyond occurrence of corrosion induced cover cracks.

This paper presents a nonlinear fracture mechanics analysis of a part of an offshore concrete structure. The analysis focuses on the risk of cracking between the prestressing ducts in the shaft of the submerged platform. The influences of water and grout pressure in prestressing ducts have been taken into consideration. The analysis has been performed using both discrete and smeared crack analysis.

This paper presents a non-contact measurement approach, based on digital photogrammetry,applied to the experimental study of the bond behavior of fiber reinforced cementitious matrixcomposite (FRCM) - concrete joints tested in single-lap direct shear tests. The use of digitalphotogrammetry techniques and traditional contact measurement approaches for determiningdisplacement and strain are investigated and compared. The results show that measurements ofstrain in the fiber bundles determined using the image correlation system (ICS) correlate well withthose obtained from electrical strain gauges. However, differences of 38% to 52% were observedbetween the maximum strain measured with either ICS or electrical strain gages attached to thefiber bundles and the maximum strain in the fiber bundles computed from the maximum appliedload. ICS is also used to measure slip and strain of bare fiber bundles, and results show that theload distribution among fiber bundles is non-uniform. The proposed measurement approach showshigher spatial measurement resolution and increased accuracy compared to traditional contactapproaches by enabling measurements in each fiber bundle and overcoming the need to attachadditional elements to the tested specimen.

Adhesive joints have been known and applied for timber structures for decades. Hybrid joints with glued-in rods are nowadays successfully used for both constructing new and strengthening existing timber structures. Since the 1980s the research and development of timber joints with bonded-in rods have been going on, however agreement regarding design criteria for these connections has not been reached. Today, connections with glued-in rods are not included in the European design code. Thus, it is desired to gather the current state of knowledge to enable application in practice of the existing and documented knowledge and experience. This paper summarizes practical and theoretical approaches from research done regarding joints with glued-in steel rods mostly in Europe and published in English, German or Swedish. The review considers manufacturing methods, mechanisms and parameters governing the performance and strength of the joints, theoretical approaches and existing design recommendations.

Determining the mechanical properties of cross-laminated timber (CLT) panels is an important issue. A property that is particularly important for CLT used as shear walls in buildings is the in-plane shear modulus. In this study, a method to determine the in-plane shear modulus of 3- and 5-layer CLT panels was developed based on picture frame tests and a correction factor evaluated from finite element simulations. The picture frame test is a biaxial test where a panel is simultaneously compressed and tensioned. Two different testing methods are simulated by finite elements: theoretical pure shear models as a reference cases and picture frame models to simulate the picture frame test setup. An equation for calculating the shear modulus from the measured shear stiffnesses in the picture frame tests is developed by comparisons between tests and finite element simulations of the CLT panels. The results show that pure shear conditions are achieved in the central region of the panels. No influence from the size of the tested panels is observed in the finite element simulations.

Currently, no appropriate standard exists that describes how to determine the in-plane shear stiffness for cross-laminated timber (CLT) panels, meaning that, there is a lack of appropriate and reliable test methods. In this paper, two gross shear test methods are evaluated: a picture frame test and a diagonal compression test, which are intended to measure the shear stiffness of a whole CLT panel. This evaluation aimed to compare the shear modulus, the amount of compression/tension in the diagonal directions of the panels and the deformations of both sides of the panels. The picture frame test and diagonal compression test provides a bi- and uniaxial pre-stress, respectively. A total of 30 non-edge glued CLT panels were tested, 17 3-layer and 13 5-layer panels. The shear modulus for the 3- and 5-layer non-edge-glued panels were measured as 418 and 466 MPa, respectively, in the picture frame test. In the diagonal compression test, the shear modulus was measured to substantially higher values of 530 and 626 MPa for the 3- and 5-layer panels, respectively. In the picture frame test, panels were equally stretched along one of the diagonals as they were compressed along the other diagonal, which was not the case for panels in the diagonal compression test. The test results also showed that measuring only one side incurs a risk of over- or under-estimating the in-plane shear modulus. Compared with results from the literature, the picture frame test seems to be a more reliable test method than the diagonal compression test.

Cracking of concrete must be avoided during the hardening phase in order to minimize the risk of durability problems in the future, such as corrosion of the reinforcement, water tightness and damages due to frost. Estimation of the risk of early age cracking requires knowledge of the combined effects from temperature development and mechanical behaviour during the hydration. In the present paper, the influence of fly ash on the young concrete behaviour has been investigated. The concrete is based on a Swedish cement aimed for civil engineering structures, and the fly ash is of class F. A comparison of crack risks between concrete containing fly ash in different amounts with concrete without fly ash is presented. Also a previously tested concrete containing limestone filler is considered. The fly ash was added to replace a part of the aggregate, which gives a higher heat evolution. However, a numerical stress analysis showed that the risk for early age through cracking for a typical civil engineering structure is significantly decreased in the mixes containing fly ash. The denotation typical civil engineering structure is used here for concrete structures such as tunnels, bridges, and ramps of common cross-section dimensions. In the case of fly ash added to concrete by a partial replacement of cement, the crack risk will probably be further decreased. For a self-balancing structure of young concrete there is no restraint from adjacent structures, and the temperature and moisture gradients within the young concrete cause self-stresses governed by equilibrium with zero external forces for any cut. The estimated risk for surface cracking on a self-balancing wall or slab was not improved by an addition of fly ash. It is probably an effect of the increased heat development, which most likely counteracts the positive effect of the increased early age creep for concrete containing fly ash. If the heat evolution decreases when cement is partly replaced with fly ash, the use of fly ash might reduce the risk of surface cracks.

This paper concerns the influence of fines from manufactured aggregates on the rheological properties of the micromortar phase of concrete. Fines from nine different aggregates were included in the experimental work. The zeta potential of five of them was measured at different additions of superplasticizer in order to study the interaction between the surface of the fines and the superplasticizer. The rheological properties of the micromortars were studied at different volume concentrations of fines and at different concentrations in the paste phase, i.e., w/c ratios. Furthermore, the micromortars were studied at different dosages of a superplasticizer. The results show that the fines have different surface properties, i.e., zeta potential, and indicate that the superplasticizer only is adsorbed on some of them. The results from the rheological characterisation of the micromortars indicate that the higher water demand of concrete with manufactured aggregates partly can be traced to the properties of the micromortar phase of the concrete.