Influence of substrate and sand characteristics on Roman cement mortar performance

When formulating repair mortars standard test specimens should be used with caution as these cannot be considered representative of samples of mortars collected on site. This work reports an approach to repair mortar formulation which takes into account the influence of porous substrates, sand characteristics and mortar thickness on the properties of both fresh and hardened Roman cement mortars. It is shown that mortars cast on a dry absorbent substrate show modified properties such as increased strength and decreased water absorption coefficient, the degree of which is a function of sand grading and surface characteristics, sample thickness and substrate sorptivity

Low energy pre-blended mortars: Part 2 – Production and characterisation of mortars using a novel lime drying technique

The presence of free water in mortars destined for silo or bagged storage can lead to the degradation of the binder phase. Such water may be present as a result of using wet, as-delivered sand or as a consequence of prior processes such as de-activation of Roman cement. Thus, water must be removed from the system prior to storage. Part 1 of this paper describes the control of a technique by which quicklime is added to the wet system which principally dries it by both slaking the quicklime and evaporation as a consequence of the exothermic slaking reaction. Two examples of mortars are presented in which excess water is removed from the system by the inclusion of quicklime. In the first, the water is present in the as-delivered sand and the binder is a combination of the slaked lime and ggbs. In the second, the water remains after pre-hydration of a Roman cement which is a process to retard its rapid setting characteristics. It is shown that optimally dried mortars are not subject to degradation following storage of both mortar types

Influence of different types of solvent on the effectiveness of nanolime treatments on highly porous mortar substrates

Historic calcareous structures suffer from weathering processes that result in the loss of some of their original properties. Nanolime products represent an attractive choice for the consolidation of these substrates containing calcite due to their high chemical compatibility with the original structure. The effectiveness of nanolime products has been widely proven for superficial consolidation treatments (e.g. plasters and wall-paintings). However, its consolidation mechanism in highly porous substrates (e.g. limestones or lime mortars) still needs to be fully understood. The aim of this paper is to study the influence of different types of solvent on the effectiveness of nanolime treatments on highly porous lime-mortars. The consolidation effectiveness is investigated by evaluating changes on superficial cohesion, porosity, drilling resistance, water absorption by capillarity, drying rate and aesthetic properties. Results showed that nanolime dispersed in a mixture of isopropanol (50%) and water (50%) yielded slightly better consolidation properties in terms of reduction in porosity, increase in strength and penetration within coarse lime-mortars than nanolime dispersed in other solvents

Influence of the combination of Roman cement and lime as the binder phase in render mortars for restoration

It is known that lime was added to historic Roman cement render mortars. The focus of this work is the influence of the combination of NHL5 and CL90 with Roman cement in mortars for restoration; however, the results indicate a wider potential for render applications in general. It is shown that simply adding lime to Roman cement does not retard its hydration and yields mortars where the binding action of the cement is compromised by the mixing process. If the cement is retarded by means of a pre-hydration process, hybrid mortars can be produced with improved workability and workable life as well as permitting the fine control of strength and moisture transport

Electric curing parameters of mortar and its mechanical properties in cold weather

Thermal curing is an effective way to accelerate the curing of cementitious materials and can be used for concreting in cold weather, in order to prevent frost damage. This study investigates electric-thermal process curing of mortar at 20 °C and −10 °C. Fresh mortar specimens were subjected to different electric potential differences and their internal and top surface temperatures were monitored using a thermocouple and a thermal camera, respectively. A theory for predicting the temperature increase of the mortar based on the applied electric parameters was developed. Furthermore, the system was used to maintain the internal temperature of mortar specimens at 10 °C for 12 h while these were exposed to −10 °C inside a cold room. Compressive and flexural strength results show that electric curing can prevent frost damage. For example, 28 days compressive strength of normally cured mortar specimens exposed to −10 °C was 27.2 MPa while mortar specimens subjected to electric curing achieved a compressive strength of 51 MPa. Results from mercury intrusion porosimetry tests showed an increase in porosity for normally cured specimens, which was responsible for strength loss

Pre-hydration as a technique for the retardation of Roman cement mortars

The setting of Roman cement is so rapid as tomake the use of retardation essential inmost practicalmortars. This work reports an approach to retardation of Roman cementmortars by means of a pre-hydration process in which pre-determined amounts of water (de-activation water) are added to the cement prior to subsequentmortar formation. It is shown that this process yields bothmonocarboaluminate and a carbonated AFm phase, the balance of which is modified by storage time; the belite phases are not affected. Increases in both de-activation water and pre-hydratedmix storage time yield a longer workable life and slightly lower strength of the mortar. An increase in de-activation water also yields an increase in shrinkagewhilst an increase in storage time results ina reduction in shrinkage. Other parameters such asmixing protocol and re-mixing affect workable life without compromising the strength