Modelling the compressive mechanical behaviour of granite and sandstone historical building stones

Building stones, particularly sandstone and granite, are very important in the building elements of Portugal’s historical and cultural heritage. Experimental research, based on uniaxial compressive tests, was carried out on selected representative samples of lithotypes of rocks used in historic built heritage, with a view to evaluating the compressive mechanical behaviour of different building stones. The results showed that porosity plays a central role in the compressive behaviour of granites and sandstones. As porosity can be evaluated in field conditions with non-destructive tests it was decided to derive an analytical model to predict compressive behaviour based on the knowledge of porosity of the building stones. A cubic polynomial function was adopted to describe the pre-peak regime under compression to implement the model. Furthermore, a statistical correlation between mechanical and porosity data had to be defined. Good agreement between experimental and analytical compressive stress-strain diagrams, from which the mechanical properties like compressive strength and modulus of elasticity can be derived, was achieved.     

Molecular monitoring of the microbial dynamics occurring on historical limestone buildings during and after the in situ application of different bio-consolidation treatments

Microbially Induced Carbonate Precipitation is proposed as an environmentally friendly method to protect decayed ornamental stone and introduced in the field of preservation of Cultural Heritage. Recent conservation studies performed under laboratory conditions on non-sterile calcarenite stones have successfully reported on the application of a suitable nutritional solution, inoculated and non-inoculated with Myxococcus xanthus, as a bioconsolidation treatment. Furthermore, this procedure has been applied in situ, very recently, to selected historical buildings in Granada, Spain. For the first time, we evaluate the efficiency and risks of the in situ application of the above mentioned treatments onto two historical buildings in Granada. The evaluation consists of a detailed investigation of the micro-biota actively growing during the seven days of the treatments - short-term monitoring and of that remaining on the stones after six and twelve months of the application - long-term monitoring. A molecular strategy, including DNA extraction, PCR amplification of 16S rRNA sequences, construction of clone libraries and fingerprinting by DGGE (Denaturing Gradient Gel Electrophoresis) analysis followed by sequencing was used to gain insight into the microbial diversity present on the differentially treated stones. The monitoring of M. xanthus was performed by PCR using species-specific primers. Similar dynamics were triggered on both buildings by the application of the nutritional solution (inoculated or non-inoculated). 16S rDNA sequencing revealed the dominant occurrence of members belonging to the Firmicutes and Proteobacteria during the seven days of the treatment, whereas after one year the order Bacillales of the phylum Firmicutes was the predominantly detected microorganisms. M. xanthus could be detected only during the seven days of the treatment. The treatments seem to activate no dangerous microorganisms and furthermore, to select the remainder of a homogeneous group of carbonatogenic bacteria on the stones after a long period of time.     

Characteristics of carbonate building stones that influence the dry deposition of acidic gases

The behaviour of several porous carbonate building stones used in Spanish and English monuments was compared. Stones were exposed to urban and suburban environments and subjected to simulated SO₂ atmospheres in the laboratory. Physical properties that affect the transfer of moisture were determined before and after exposure, and related to the degree of reaction of the stones. The degree of reaction was determined by analysing the reaction products. Results showed that physical properties influenced the reactivity of the stones. These characteristics also changed as the stones weathered due to the different concentrations of impurities in the material. Moreover, stones with a high specific surface area and/or a deliquescent salt content may promote more NO_x dry deposition.     

Assessing alkali-silica reaction damage to concrete with non-destructive methods: From the lab to the field

The effectiveness of any non-destructive (ND) procedure for evaluating the damage to concrete depends on the relation between physical and mechanical properties. With this attempt, this paper deals with the application of three ND methods (ultrasonic wave velocities, dynamic Young modulus measured with resonant frequency and electrical resistivity) for the evaluation of concrete cores drilled from a large hydraulic structure affected by alkali-silica reaction (ASR). In parallel, the concrete was tested for its mechanical properties and petrographic examinations were also performed. ND results were compared with those obtained from concrete specimens made in the lab and showing various levels of deterioration associated with ASR.Results from all methods (except electrical resistivity) showed that the overall condition of the concrete remains of good quality, in spite of the significant expansion rates measured on the structure. On the one hand, damage is mainly located within the first two meters from the surface. On the other hand, concrete deterioration at the bottom of the structure was very low.The electrical resistivity did not appear to be appropriate for evaluating the damage level related to ASR. Dynamic Young modulus and ultrasonic pulse velocity yielded better results. The best correlation was obtained between the P-wave velocities and the static Young modulus. This study emphasizes that laboratory results cannot be directly extrapolated to field results.     

Effect of salt crystallization on stones of historical buildings and monuments,Konya, Central Turkey

In this study, we investigated the chemical and physical properties of the volcanic rocks used as building stones in historical places and monuments. The chemical weathering effect of salt crystallization on these stones was measured on the laboratory conditions (in most cases, used samples were very small). For this purpose, the dry weight loss (DWL) test was conducted. The rocks of dacite, andesite and tuffs of volcanic origin have different durability against salt crystallization. The most stable rocks are dacites (DWL 2.06%) which were used in the construction of Hittite monuments at Eflatun. The durability of the stones is closely related to their chemical, mineralogical, petrographical and mechanical properties. The stones used in the historical buildings are generally much more stable than present-day building stones.     

Some engineering properties of natural building cut stones of Cyprus

Natural building cut (NBC) stones are being used in Cyprus for ages to build masonry structures because of being abundant, relatively easy to cut and shape and good performance in many applications. Almost all of the historical buildings in Cyprus are made of these NBC stones. Although these stones are low cost construction materials, they are not widely used in these days. This is due to lack of knowledge causing incorrect construction methods and highly skilled labour requirement.For this study two quarries are selected and samples obtained were tested for some physical and mechanical properties. Traditional names of these NBC stones are Meluşa Stone and Karpaz Stone (or Bouri Stone). The physical properties such as bulk density, water absorption, specific gravity and porosity were measured. The mechanical properties such as compressive strength, flexural strength, direct tensile strength, splitting tensile strength, point load strength, fire resistance, abrasion resistance and freeze-thaw resistance were measured. From the results obtained it can be said that Meluşa stone behaved better than Karpaz stone. A regression analysis also provided a polynomial relation between compressive strength and burning temperature and flexural strength and burning temperature.     

Comparison of Mechanical Behavior of Two Overconsolidated Clays: Yamashita and Louiseville Clays

A site investigation program was carried out at the Yamashita site, Yokohama, Japan, by means of laboratory as well as field tests. It was found from the investigation that the clayey layer is overconsolidated with an OCR of about 2.0. It is evident from geological consideration that this overconsolidation may not have been caused by stress change, but was probably due to structure effects such as cementation or delayed consolidation. The physical and mechanical properties of the Yamashita clay is compared with those of Louiseville clay, a Champlain Sea Clay widely distributed in Quebec, eastern Canada, and a well known cemented clay. Louiseville clay was retrieved by Japanese sampler and transported to the Port and Harbour Research Institute (PHRI) for laboratory investigation. Comparison of the two clays shows that strength properties such as the stress-strain curve or stress path for both clays are very similar to each other. However, the pattern of the e-log p curve measured by Constant Rate of Strain oedometer, particularly beyond the yield consolidation pressure, is remarkably different between the two clays.     

The reliability of CPTu and DMT for the mechanical characterisation of soft tailings

Nowadays, the stability and the safe cover and closure of soft tailings has become one of the most challenging topics in geotechnical and environmental engineering. For appropriate analysis and modelling, geotechnical properties of tailings should be well defined. Due to low strength, viscous nature and poor trafficability, as well as due to the specific geometrical properties of fine particles and pore water chemistry in tailings, different test methods and their modification and improvements must be used for valid and reliable characterisation of tailings. This paper analyses and compares the results of different field test methods, piezocone penetration test (CPTu), flat dilatometer test (DMT) and field vane test (FVT), performed on the red gypsum sludge and complementary laboratory tests. CPTu and DMT measurements were evaluated using procedures developed for soils and the obtained mechanical properties were compared with those measured in the laboratory. The significant distinctions between different test methods and different empirical correlations were analysed taking into account differences in index properties of soils and the red gypsum sludge. Based on analysis, some modifications of conventional empirical correlations were proposed for field tests results interpretation and sludge characterisation. The obtained data also show the advantages and limitations of some conventional methods and prove the need for further development in that field of geotechnical investigation.

     

Estimation of thermophysical properties using natural signal analysis with heat and moisture transfer model

Conduction heat transfer through opaque envelope components characterizes the thermal performance of buildings and its consequences in terms of energy consumption and thermal comfort. A building envelope can be thermally described by two parameters: thermal conductivity (λ) and heat capacity (ρ·c). Estimating these thermal properties in situ allows the characterization of real building elements considering different aspects, such as thermal behavior under specific weather conditions, quality variability in materials, local construction technologies and material deterioration. This paper presents a method to estimate the thermal conductivity and volumetric heat capacity of a homogeneous element using a non-destructive test considering natural oscillations. Surface temperature and heat flow are measured in a concrete sample (with known thermal properties) and the data is treated with a signal processing technique. Estimation is carried out with a heat and moisture transfer model. Measurements were performed on six separate days under different sky conditions within a period of one month, to determine the importance of solar radiation as a heat source. Results gave acceptable estimates (average inaccuracy of 10-14%) of both thermophysical properties.     

Development of a penetration test for timber impregnation products for use in old buildings

This paper studies the application of commercial biocides to old maritime pine timber structures (Pinus pinaster Ait.) that have previously been impregnated with other products. A method was developed in the laboratory to be used in situ to determine the impregnation depth achieved by a new generation biocide product applied to timber from an old building. This timber had once been treated with an unknown product difficult to characterize without extensive analysis. The test was initially developed in laboratory conditions and later tested on elements of the roof structure of an 18th century building. In both cases the results were promising and mutually consistent with penetration depths for some treatments reaching 2.0 cm. The application in situ proved the test’s viability and simplicity of execution giving a clear indication on the feasibility of possible re-treatments.     

Predicting uniaxial compressive strength,modulus of elasticity and index properties of rocks using the Schmidt hammer

The Schmidt hammer test is a non-destructive method which can be used in both laboratory and field to provide a quick and relatively inexpensive measure of rock hardness. The study investigated the relationship between the Schmidt hardness and modulus of elasticity, uniaxial compressive strength and index properties of nine types of rock including travertine, limestone, dolomitic limestone and schist. The empirical equations developed indicated the Schmidt hardness rebound values have a reliable relationship with the uniaxial compressive strength of rock (r = 0.92). Comparing the results with those reported by other researchers, it is concluded that no single relationship can be considered reliable for all rock types. Whilst the equations developed in this study may be useful at a preliminary stage of design, they should be used with caution and only for the specified rock types.      

Characterizing cyclic and static moduli and strength of compacted pavement subgrade soils considering moisture variation

Compacted soils are widely used as the subgrade layer for pavements. Knowledge of the mechanical properties of subgrade soils under cyclic and static loading conditions and their variation under the influence of environmental factors is required for the rational design of pavements based on mechanistic methods. This paper presents an experimental investigation of the cyclic and static moduli and the strength properties of seven different compacted Canadian subgrade soils considering the variation in the post-compaction moisture content. Cyclic triaxial tests were performed to reliably determine the resilient modulus (M_R). Unconfined compression tests, which allow an unloading-reloading loop at 1% strain, were performed to determine the deviator stress (S_u1%) at 1% strain, the reloading elastic modulus (E_1%) at 1% strain and the unconfined compressive strength (q_u) at failure. The physical properties, the chemical and mineralogical compositions, and the soil-water characteristics of these soils were also determined. Relationships were developed to predict the M_R from the S_u1%, E_1%, q_u and soil physical properties for the investigated subgrade soils because the experimental determination of M_R is both expensive and time-consuming. The studies presented in this paper provide useful information and approaches that can be used to promote the implementation of mechanistic pavement design methods using simple techniques.     

Sediment oxygen demand techniques: A review and comparison of laboratory and in situ systems

Sediment oxygen demand (SOD) measurement techniques are reviewed and suggestions offered for improving their performance, including an experimental approach toward standardizing the SOD methodology. Five principal analytical systems are used to evaluate SOD. These are conveniently classified as: (1) batch (laboratory and in situ); (2) continuous flow; (3) manometric; (4) electrolytic and (5) dehydrogenase activity. Comparison of SOD methods requires establishing certain criteria which should be met for a given method to be considered acceptable. These criteria are: (1) consistency; (2) reproducibility and (3) efficiency. Laboratory techniques can meet the acceptability criteria more easily than in situ techniques. A SOD reaction chamber used in our laboratory provided reproducible data for replicate analyses of stream and lakes sediments and met our acceptability criteria.     

The measurement of benthal respiration

This paper reviews the methods used in the measurement of benthal respiration. The disadvantages of laboratory methods are stressed, in particular the technical problems in simulating flow over the substratum. Two in situ methods are described for use in lakes and streams and the results of these are compared with laboratory methods using an oxygen budget as an independent check.     

Evaluating and comparing different methods and models for generating relaxation modulus master-curves for asphalt mixes

Based on a master-curve, mixture properties can be predicted or interpolated at different temperatures and loading times of interest from a limited set of laboratory test data. This paper presents a comparative assessment of three methods used for generating the relaxation modulus (E(t)) master-curves of hot-mix asphalt (HMA). These methods were the Arrhenius, the Williams–Landel–Ferry (WLF), and an optimization technique with the sum of square error (SSE) method. Experimental data (E(t) values) for different HMA mixtures were gathered by performing uniaxial loading (strain-controlled) relaxation modulus tests (RMT). The process for evaluating the three methods was based on using the same RMT laboratory data to generate E(t) master-curves and then comparing the best fit functions. Corresponding results suggested that the SSE method generated the best fit functions relative to the measured E(t) data. Unlike the Arrhenius and WLF models, the SSE is independent of external empirical material constants in its application and is universally applicable to any given material or HMA mix type. However, this study also demonstrated that both the Arrhenius and WLF methods can produce satisfactory (and in fact equivalent results) if appropriate constants, that are material or mix type specific, are used. Conclusively, the findings of this paper suggested that satisfactory application of the Arrhenius and WLF methods should be with caution, in particular with respect to the material constants. Otherwise, the SSE method proved to be more accurate and would be preferred.     

Experimental investigation on mechanical properties of binary and ternary blended pervious concrete

The purpose of the investigation was to study the effect of binary and ternary blends of cement on the mechanical properties of pervious concrete (PC) specimen through destructive (DT) and non-destructive testing (NDT). Various combinations of fly ash (FA), limestone powder (LP), metakaolin (MK), and silica fume (SF) as mineral admixtures have been investigated to partially replace the cement up to 30% by weight in PC. Standard cube specimens of size 150 mm × 150 mm × 150 mm of binary and ternary blends of mineral admixture of pervious concrete were prepared to conduct standard compressive strength test and split tensile test at 7 and 28 days of curing. The ultrasonic pulse velocity (UPV) test and Rebound Hammer test were used as a non-destructive testing tool to substantiate the robustness of PC and to determine the approximate mechanical properties where other destructive testing tools are not feasible in case of in-place pervious pavements. Overall the pervious concrete made with LP based ternary blends (PLM and PLS) were found to perform better than FA based ternary blends (PFM and PFS) and control mix (PC) in destructive and non-destructive testing.     

Mechanical performance of BStIV grade steel bars with regard to the long-term material degradation due to corrosion damage

The mechanical performance of BStIV grade reinforcing steel bars from four different manufacturers was experimentally investigated and evaluated by exploiting the performance indices concept. The experiments included tensile tests, carried out on uncorroded and pre-corroded steel specimens. To corrode the specimens, accelerated laboratory corrosion tests were involved. The later tests were made to assess the expected degradation of the materials mechanical performance with accumulating corrosion damage during the life of a reinforced structure. For the evaluation of the mechanical performance, index Q_D has been introduced. The index Q_D considers the combination of tensile strength and tensile ductility in a single quantity by accounting also for scatter in material’s mechanical properties. Index Q_D can be applied to assess the materials mechanical performance both in the undamaged and in the corroded conditions. In both cases, the materials were ranked based on the outcome of the evaluation of their mechanical performance. Subjective choice is needed in order to consider the effect of corrosion damage on the material’s mechanical performance.     

Marginal lateritic soil/crushed slag blends as an engineering fill material

Lateritic soil (LS) with suitable mechanical properties is commonly used as the subbase and as engineering fill material in roads. However, LS is becoming increasingly scarce as a source for road projects. The usage of marginal LS as a pavement subbase and engineering fill material leads to some challenging issues that this research seeks to address. This paper evaluates the possibility of using crushed slag (CS), a waste by-product, as a replacement material to stabilize marginal LS for engineering fill applications. An investigation was undertaken on the physical and mechanical properties of the LS/CS blends at various CS replacement contents. The laboratory evaluation program included particle size distribution, specific gravity, water absorption, Los Angeles (LA) abrasion, Atterberg limit, California Bearing Ratio (CBR) and swelling tests. CS replacement was found to reduce the fine content and increase the abrasion resistance of the marginal LS, resulting in a reduction in liquid limit, plasticity index, LA abrasion and particle breakage. With increases in the CS replacement content, a marked improvement in the physical properties of the blends was found, including increased soaked CBR and reduced swelling. Normalized CBR_CS/CBR₀ and S_CS/S₀ and CS replacement relationships were developed in this research. CBR_CS and S_CS are the CBR and swelling values at various CS replacement contents, respectively and CBR₀ and S₀ are the CBR₀ and swelling values at a 0% CS replacement content, respectively. The results are expected to be of interest to both geotechnical and pavement practitioners. The physical and mechanical properties of the blends with a minimum of 10% CS replacement content were found to meet the national local road authority requirements for engineering fill material.     

A practical approach to in-situ evaluation of surface-treated structures

This paper describes the result of a field evaluation carried out to ascertain the effectiveness of hydrophobic and consolidating treatments applied to the surfaces of three historic buildings and monuments in the UK. The surface treatments were 7–18 years old at the time of testing. The field trials were carried out using a simple but practical suite of complementary and wholly non-destructive test methods. The methods, procedures and criteria used for assessing the performance of surface treatments used were developed from an EC sponsored laboratory and site test programme carried out on stones representing those used in the construction of monuments across Europe. This approach has been shown to provide useful, early warning information to owners of historical or modern structures, which will enable them to make an informed decision regarding when to treat a deteriorated surface or the need to re-treat an already treated but subsequently weathered surface. The results obtained suggest that the treatments applied on some of the tested structures have deteriorated to the extent that it is now time to consider re-treatment.