Category Advances in. Engineering Structures,. Mechanics &. Construction

Mechanical Characterization of HPC with Limestone Filler

Technical literature on new generation of HS/HPC is available since a decade or more, with sev­eral examples of structural applications (Aitcin, 1999; Rols et al., 1999; Person, 1998; Toutanji et al., 1995; Rosati, 1999; Guerrini et al., 1999; Namiki, 2005; Nawy, 2001). The most significant mechanical parameters of the today well known HPC, refer to strength giving less attention to elastic modulus, or other characteristics related more to workability and durability. Because many characteristics of high performance concretes are interrelated, a change in one usually results in changes in one or more of the other characteristics. Consequently, if several characteristics have to be taken into account in producing a concrete for the intended application, each of these characteristics must be clearly specified in the contract documents. That is why the design documents of the two mentioned interventions should refer to a Guideline documents based on experimental investigations

Table 4. some significant figures of Limestone Concrete samples.

Time

(Days)

Compressive strength (MPa)

Flexural tensile strength (MPa)

Dynamic elastic modulus (MPa)

1

80

10.8

43,491

2

91

15.2

44,900

7

103

18.9

46,000

28

118

20.6

48,100

Fig. 7. Technical problems related to silica fume utilisation: plastic shrinkage (constant water/binder ratio) (Cangiano, 2005).

on different mix design best suited for different structural elements of a complex whole building, like are, for examples, underground retaining elements, underground elements in presence of water, floor slab elements, linear horizontal elements, vertical “core” elements. In particular the paper wants to introduce, as mentioned before, the campaign of tests aiming to produce large and well defined spectrum of mix design for particular HS/HPC based on fine aggregate of limestone. LSC’s are classified as HS-HP concretes, with the advantages of being characterized by the complete absence of pozzolanic addition, i. e. silica fume, generally present as filling material in practically all type of HPC (De Larrard, 1993; Toutanji, 1995). Table 4 shows some first results of the mean significant mechanical characteristics of Limestone Concrete, and allows us to include Limestone Concrete in the range of HS/HPC, with advantages of being Self-Levelling and Rapid Hardening Concrete (Plizzari et al., 2003).

It is however recognized that the following problems are related to silica fume utilization: (a) the high cost (about 4-5 times the cost of cement), (b) the total shrinkage (plastic and hydraulic) of HPC containing silica fume (10%) may be greater than other HSC based on other mineral admixtures,

(c) HPC with silica fume may exhibit a high tendency to desiccation and hence to early micro­cracking, as a consequence the long term durability may suffer, (d) several researchers found a loss of compressive strength between 90 days and 4 years of concrete with silica fume. Figure 7 underline the problems related to shrinkage behaviour when utilizing silica fume and concrete mix designs according to European Code (EN No. 197).

The main task of the experimental research on new generation of HSC using limestone (without any content of silica fume), is to identify a size distribution curve of the system composed by cement and aggregates in order to produce HPC’s characterized by: (a) very good rheological properties and

Fig. 8. Strength development of two different mix of LSC.

Fig. 9. The favourable performance of LSC respect to hydraulic shrinkage.

(b) rapid development of mechanical performances. In this starting-up phase of the experimental research, just few mix have been proposed and tested with the primar goal to prove the sensibility of the mechanical characteristic to small variations of size aggregates in the early stage.

The graphs and table of Figure 8 show the upper and lower bound of the strength development performance due to slightly different mix, where it is clearly show the rapid hardening characteristic of Limestone Concrete mix.

The favorable performance of LSC respect to shrinkage behavior is summarized in the graphs of Figure 9 where LSC is compaired with different mixes of SCC.

Further development of the research will be focused on obtaining LSC with specific characteristic for the specific used, identified as follows:

– for beams, pillars and floor-slabs ^ LSC with properties of HSC and RHC;

– for “core” structure ^ LSC with high resistance to temperature and with high toughness;

– for conteining walls ^ LSC with properties of durability against salts, very low permeability, low hygrometric shrinkage.

In any case Limestone Concretes, also fiber added, should develop creep characteristics as good as those of SCC.

Conclusions

The paper starts from the assumption that the use of high-strength, high-performance concrete (HS-HPC) is rising up, not only for pillars, in high-rise buildings. The research program undertaken by Politecnico di Milano-Universities of Bergamo and Brescia, which starting-up phase results are here reported, is primarily focused on Limestone Concrete samples tests, to state the mechanical characteristics requested not only by new codes, but also by new building design philosophy in case of high-rise buildings. As a matter of fact, the research on the scaled structural elements (wind test), or/and on numerical models simulating structural elements under impact or blast loading condition will be a necessary completion in the overall knowledge for the optimization of strength and per­formance capacity of the new HPCSs and their selected use. The complete range of knowledge may produce a material highly competitive for the bearing structure of the high-rise buildings.

[1] the grouted pocket foundation (PF) solution showed the smallest strength degradation during the cycles. The column strength at the 5% drift cycles is equal to 82% the maximum column strength. Collapse was reached during the first cycle at 5.5% (168mm), due to buckling of the longitudinal bars. Specimen PF showed the most stable behaviour up to collapse among all of the specimen tested;

• all of the grouted sleeves (GS) column-to-foundation connections showed a considerable strength degradation during the cycles. In all cases, the strength of the column at the 5% drift cycle was approximately equal to 2/3 the maximum strength. The maximum strength at the 2.5% drift was approximately equal to 90% the maximum strength. The observed strength degradation is due to the progressive damage of the 20 mm grout layer existing between the precast column base and the foundation. This grout layer eventually crushed and was expelled

[2] Since the conventional and shear modes are not identified jointly, the overall matrices [C;k] and [Bk are not diagonal – only their principal sub-matrices exhibit this property.

[3] Although most of the novel GBT formulations have not yet been applied to other than isotropic and linear elastic members, this is a straightforward (even if time-consuming) task that is planned for the near future.

[4] No validation is presented for the elastic-plastic GBT-based results, as the authors know no commercial FEM code capable of calculating plastic bifurcation moments – e. g., neither Adina (Bathe, 2003) nor Abaqus (HKS, 2002) offer such possibility.

[5] It was found that the shear modes associated with non-linear warping (see Figure 9) do not contribute to the beram fundamental vibration modes. Nevertheless, they were included in all analyses.

[6] crushing in the angle legs denoted by the ultimate tension stress being reached in the angle legs parallel to the beam web (conservative);

• crushing in the beam web denoted by the ultimate tension stress in the beam web being reached (again, conservative);

• 20% increase above the ultimate bolt shear stress magnitude.

The initial stiffness, KC1 , is defined using the smaller two stiffness magnitudes. The first is based upon web yielding and the second is based upon angle leg yielding. Post-yield stiffness is defined rather arbitrarily using a 0.5% multiplier to account for moderate strain hardening in the material on the way to crushing.

It should be noted that the behavior of the supporting element (e. g. a column flange, a column web, a girder flange) is omitted. This is likely very important, but the complexity incurred through consideration of this behavior would render the analysis proposed intractable. Expected yield and ultimate tensile stresses for the materials are used as recommended in the GSA guidelines (GSA 2003). Further details of the formulation and example computations can be found in Foley et al. (2006).

The tension and compression response for the bolt elements are shown in Figure 6 for the W18x35 and W21x68 wide flange shapes, respectively. These wide-flange shapes are consistent with the 3-story SAC-FEMA Boston building assumed as the analysis prototype (FEMA 2000b; Foley et al. 2006).

[7] if the current stress point is on the memory surface and (———– ) t ■ dah > 0, this signifies a

daij aij J

loading case;

if the current stress point is on the memory surface and loading to unloading occurs;

if the current stress point is inside the memory surface, i. e. – a (aj) – Rmem < 0, it is then an unloading case.

For the loading case the spring stiffness of the ‘Kelvin-Voigt type’ elements is defined as a function of the equivalent stress, Et = E1(aeq). For the unloading case, it is assumed that Ei remains the same

during the entire unloading process, and its value is that of the Et at which the switch from loading to unloading took place.

[8] In the sequel we write „displacements”, „strains”, „stresses” and „loads” having in mind generalized variables taken usually in Structural Analysis.

[9] For structures made from the rigid-perfectly plastic material the kinematic unknowns Я, w should be replaced by their rates Я, w.

[10]I. e. STL files that will procure a successful build on a Rapid Prototyping machine.

[11] Exposure (15 ± 1) h at a temperature (+40 ± 2) °C

• Change within (60 ± 20) min to a temperature (-20 ± 3) °C; exposure (2 ± 1) h

• Change within (80 ± 20) min to a temperature (+70 ± 2) °C; exposure (4 ± 1) h

• Change within (60 ± 20) min to a temperature (+40 ± 2) °C

The pictures in Table 1 show selected specimens after 25 cycles given above. All specimens showed large-area debondings; partly microcracks occurred in the Lexan PC which were availed by the surface pre-treatment. The wished compound effect could not be achieved. The experimental program was changed with regard to plastic, surface pre-treatment and adhesive.

In Table 2 shows specimens of another series of experiments with changed adhesives and surface pre­treatment methods. Using the Pyrosil method had a very positive influence on the compound effect between glass and plastic. In this process a pre-treatment of the glass surface as well as of the plastic surface was carried out. The Pyrosil method produces an increased surface energy and thus improves the bonding.

After 25 cycles no microcracks or debondings occurred in polycarbonate Makrolon GP 099 (see Table 2, specimen 3-3). In the case of polycarbonate Lexan PC (see Table 2, specimen 4-3) microcracks oc­curred and – at the edge – debondings.

In addition to an acrylic adhesive two other adhesives were deployed (Epoxy and PUR). Both speci­mens showed large-area debondings leading to the destruction of the glass in the case of specimen 6-3. Both adhesives are probably not adequate to produce a durable compound between glass and Lexan. The Pyrosil method had no influence on the compound effect.

Main Structural Material Performances for New High-Rise Buildings

Some background considerations, from literature and from direct experiences here reported (Namiki, 2005), states that the improved new generation of High Performance Concrete (HPC) may lead the concrete to be highly competitive in respect to different materials, if the material performance is optimized taking account the response of the structure under the following actions:

(a) the structural behavior under wind actions,

(b) the structural behavior under explosion and impact actions,

(c) the behavior under cyclic and/or alternate loadings,

(d) the shrinkage and creep behavior.

Recent investigations comparing the different performances of various building materials can be summarized in Table 1, where the signs +, 0, – indicate respectively good, neutral, bad performance. High Strength Concrete (HSC) shows positive performances respect to the entire spectrum of the chosen criteria (Chew Yit Lin, 2003; High-Rise Manual, 2003; Taranth, 1988).

Table 1. Comparison on different materials frame construction.

Criteria

Reinforced concrete, Normal-strength concrete

Reinforced concrete High-strength concrete

Steel

construction

Composite

construction

method

Construction costs

+

++

0

+ +

Weight of construction

0

+

+ +

+

Stiffness

++

++

0

+

Flexibility of plan

0

0

+ +

+

Behavior in fire

++

++

+

Construction time

+

+ +

+ +

Usable area

+

+ +

+

SCORE

5

9

7

9

Taking moreover a particular look, for example, to the specific criteria identified as “construction cost” and “construction time”, Tables 2 and 3 show significative data (High-Rise Manual, 2003). Table 2 indicates sharp favourite performances by using HSC for the structures, not only considering the cost, but even from the point of view of the usable area needed by the structure. Table 3 is self explaining if we consider that HPC, beside improved mechanical properties, have the further relevant feature: formworks can be taken away just 24 hours after the pouring the concrete, while dealing with NSC (Normal Strength Concrete) at least 4-5 days are required. In Table 3 it is easy to observe that, while 13 working days were required to complete the rough work for a standard floor during the construction of the Dresden Bank high-rise in 1974-1979 (obsolete concrete technology + NSC), the same task is currently achieved in mere 4 working days on the Galileo site (modern concrete technology + HPC) (High-Rise Manual, 2003; The Concrete Society, 1997; Fairweather, 2004). The immediate cost construction are primarily related to the time construction. Tough steel structure is traditionally reckoned to be much faster than the concrete structure, but because of significant advantages in concrete technology, this is no more true: in fact, with concrete showing features of self-levelling (SCC), the new pumps equipment assures concrete puring even at heights of 300 m, and also because of modern formwork systems (self-climbing formwork), rapid and safe progress in the rough work is guaranteed.

Research studies carried out, and still in progress, in the field of mix-design of HSC/HPC, and related technology in the construction sites, seem to show favourable results in achieving better per­formances, i. e. rapid hardening, absence of segregation, better durability (no alcaly-silica reaction), when limestone is used as filler, as it will show in the next section.

It is worth to recall, as mentioned before, due to even the consequences of recent past accidents, that the engineering design of a land-mark buildings can not ignore the possible blast loading effects. As it is well known, the physical action on a wall F, due to a plane shock wave, generates an overpressure Ps and a drag loading Pd, according to the scheme of Figures 3a and 3b.

When an explosion occurs inside a building, then it is the interior surface of the walls and ceiling which are first loaded by the pressure of the shock wave, reflecting therefore and increasing the pres­sure. The effects on the structure may be devastating, considering in addition that, as consequence of an explosion, even fire may occur. Figure 4 shows the accident occurred in spring 2002 at the Pirelli building, headquarter of the Regional Government in Milan. The explosion of the fuel tanks of the aircraft, among other consequences, caused a permanent deformation of the 26th r. c. floor with a

Table 2. Construction costs and usable area for different structural material.

Table 3. Construction time – HPC/HSC versus steel.

Property

Height

Completion

Rough Work per Standard Floor

Business Research Center, Warsaw, Poland

104 m

2000

5 working days

Taunustor Japan Center, Frankfurt, Germany

114m

1996

4 working days

World Port Center, Rotterdam, The Netherlands

125 m

2001

5 working days

Galileo,

Frankfurt. Germany

136 m

2003

4 working days

Drcsdncr Bank, Frankfurt. Germany

166 m

1979

13 working days

Trianon,

Frankfurt, Germany

186 m

1993

5,5 working days

Millennium Tower, Vienna, Austria

202 m

1999

3 working days

Park Tower, Chicago, USA

257 m

2000

3 working days

Trump World Tower, New York. USA

269 m

2001

5 working days

Pctronas Tower,

Kuala Lumpur, Malaysia

452 m

1998

5 working days

Fig. 3. Overpressure due to plane shock wave action.

Fig. 4. Draw of the airplane impact and the permanent floor deflection.

deflection of 22 cm, but not the collapse, despite the high temperature due to fire (Migliacci et al., 2005; Kappos, 2002).

The stiffness of the structure is very significant in considering the horizontal loads, i. e. earthquake and wind actions.

• Earthquake effects: stell constructions are highly suitable in areas subjected to earthquake as steel allows the structure to absorb part of the kinetic energy produced by the earthquake in the form of plastic deformation. Technically a similar ductile behaviour can be achieved by using for the structure HSC and reinforcement steel with high strength and ductility.

• Wind effects: reinforced concrete as the merit over steel frame construction in high rise build­ings to present a less sway wind. The structural behaviour minimizing the wind effect is at best achieved by concrete displaying a high values of Young modulus.

Fig. 5. Plastic model of “City Life” project in Milan. .

Fig. 6. Plastic model of “Garibaldi-Repubblica” project in Milan.

The points so far briefly recalled seem to highly recommend the choice of using reinforced concrete structure in the engineering design for a high-rise building, with particular attention to the best suitable mix design of HSC/HPC for each different action and structural component of the building.

For these reasons, a comprehensive study on best performing HPC mix design, with particular reference to Limestone Concrete, have been requested, with the purpose to draw Guidelines for use, in the oncoming starting up design phase of two important land mark interventions in the city of Milano. Figures 5 and 6 show the plastic model of the two projects, respectively the so-called “City Life” in the former trade fair area, and the so-called “Garibaldi-Repubblica” area, both in the central part of the town.

COMPREHENSIVE STRATEGY FOR HSC BEST PERFORMANCE IN. EXTENSIVE APPLICATIONS OF LANDMARK WORKS IN ITALY

A. Migliacci1, P. Ronca1, P. Crespi1 and G. Franchi2

1 Structural Engineering Department, Politecnico of Milan, Milan, Italy
2AMiS-Structural Engineering Office, Milan, Italy

Abstract

Centering on worldwidly present urban areas, there have been many high-rise landmark buildings constructed in recent years. It is recognized that reinforced concrete has merit over steel frame construction in high-rise buildings, such as less sway in high winds, better human life protection in case of accidental heavy damage, better noise resistance. The use of high-strength concrete is rising, not only for pillars, in high-rise buildings. The paper points out on the need of classifying the HP-HSC for the different requested characteristic that materials have to exhibit on different structural elements of a complex structure. Among types of concrete, which binds together characteristics of High Strength Concrete (HSC) and High Performance Concrete (HPC), particular reference is made to Limestone Concrete (LSC).

Existing literature provides data on self-levelling, high performance, rapid hardening concrete, able to reach in few days the standard of HPC (Kelham, 1998; Montgomery et al., 1998; Nehdi et al., 1998). In particular the technology here referred for limestone concrete is not the usual one, but it makes reference to a mix design, characterized by an industrially produced limestone aggreg­ates, with total absence of Silica Fume or any other addition of pozzolanic material or accelerating admixture (Cangiano, 2005; Cangiano et al., 2004).

The paper points out the significance of Limestone Concrete, as High Performance Concrete, application, starting from the following key construction requirements: in large public works with characteristic of very high durability, the choice of a technical solution it is not at all dependent on the construction cost only. In fact in this work, life service and safety performances, that slightly increase the construction costs, are of paramount importance. Starting from this key assumption, new materials, and in particular new concretes, may be able to notably cut life service and safety costs, considerably improving the performance/cost ratio of the selected solution, due to the large cut of maintenance costs. The paper wants to briefly explain the state of the art and the today frontier which lead to the material basic choices in structural design of high-rise buildings. In particular the paper refers to a comprehensive campaign of tests, in a starting-up phase, shared among different university and private laboratories in Italy, which aims to draw Guide Lines for different specific uses of Limestone Concrete, as HPC, in different structures typologies and environmental conditions.

Introduction

Italy, like other countries in Europe, has experienced high rise building constructions with significant delay, respect to different countries all over the world. Reasons due to architectural heritage, cultural and educational schools in architecture may be the principal sources of delay. The construction of high rise buildings as new land-mark of our traditional and world-wide known cities is still a debating issue. Nevertheless, or because of that, and due to some episodes unfortunately experienced by important widely known buildings, the today technological background about the best requisites of advanced materials, as well as methods of structural analysis and design, indicates the need of significant and innovative approaches and strategies for achieving the best results for the construction

853

M. Pandey et al. (eds), Advances in Engineering Structures, Mechanics & Construction, 853-863.

© 2006 Springer. Printed in the Netherlands.

Fig. 1. The sail building phase of the Dives in Misericordia Church.

Fig. 2. WTC in San Marino construction site.

of landmark buildings, like the high-rise buildings are (High-Rise Manual, 2003; Simiu et al., 1996; Fairweather, 2004).

The solution of the engineering project of an architecture design has to be the optimal solution among several feasible solutions, often mutually contradictory and conflicting each other. Each different architectural project has own characteristic and demands for the best solution. Recent realiz­ations have been discussed as peculiar examples in Italy, as for example the “Dives in Misericordia” Church in Rome (Figure 1) or the main r. c. structures of the World Trade Center in S. Marino (Figure 2) .

Due to some innovative architectural solutions, the demand due to particular layout of the struc­tural elements or due to geometrical shape and slenderness of the vaulted structure, together with particular demand for the durability of brightness, have stimulate the research toward new techno­logical, engineering and material solutions. The best design of the so called landmark building, as the high-rise buildings mostly are, is today focused, taking advantages from previous experiences, on different main objectives. The objectives to be considered, as far as materials are concerned, are:

(a) mechanical resistance,

(b) stiffness,

(c) ductility and toughness,

(d) durability,

(e) fire resistance.

In addition the objectives to be considered in the construction site are:

(a) simplicity and easiness of the construction processes,

(b) construction immediate costs,

(c) construction time and feasibility to respect the time schedule,

(d) site job environmental impact,

(e) historical and monumental existing constraints.

The new design philosophy for landmark long-lasting architectural buildings has to take account also the objectives for the service life, from which the most significant are:

(a) construction flexibility,

(b) low maintenance costs,

(c) assurance of high safety level (human life safeguards),

(d) environmental sustainability,

(e) urban costs and constraints.

The strategy of choosing the solution has to consider all the costs among the immediate construction, the life service and the safety costs.

As it will be briefly shown in the next section, among different parameters of the optimized solu­tion, the chosen main structural material has a significant role in improving the performances/cost ratio, due to the cut of life service costs and to further advantages, like smaller dimensions of structures, reduction of construction time.

Air Samples

Although touch and building surfaces were monitored over the 18-month test period, the main interest was in the potential reduction of airborne bioburden as a result of total environmental treatment. For the treated wing, commercially available reusable air filters containing impregnated triclosan polypropylene filter fibers were selected. The control wing contained regular pleated-type disposable filters, the same type used throughout the healthcare campus in the majority of its buildings. The reusable air filters on the treated wing were removed, washed and reinstalled every four months. The disposable filters on the untreated wing were replaced every two months. A total of ten locations were selected for air testing on the treated wing with a corresponding ten on the control wing. Additional sampling was taken outdoors, as well as in the main entrance vestibule and waiting area. These were used for additional comparison with values obtained in the wings. The results for the two wings are compared in Table 3 in which the average values are reported at three equally spaced time intervals over the 18-month study period. Three reference values are provided at the bottom of Table 3 that can be used for additional comparison. These values were the average values over the entire test period. The laboratory value was normalized to 1.0 cfu/ft3 and is used in Table 3 as a base comparison. The air quality in the laboratory was considered as one of the best or preferred levels of air quality on the campus.

It is apparent from Table 3 that the treated wing was maintained at a much ‘cleaner’ level than the control wing throughout the test period. Overall, the results indicate a consistent reduction of

total bioburden with time in the treated wing. There was a consistent reduction and stabilization after 12 months. Air quality was remarkably good and remained close to that found in the microbiology lab. In contrast, the bioburden in the untreated wing appeared to increase continuously with time. Although the level of bioburden in the untreated wing at 18 months was only 42% of the value found in the front entrance vestibule, it was 2.4 times higher than the treated wing and continued to increase. Since this was a new building and the level of airborne bioburden could continue to change with age, it is conceivable that the untreated wing could continue to increase in bioburden well above the value reported. In contrast, it is possible that the treated wing could level out, at or about the level found at the end of this study. That level was only 17% of that of the vestibule and only 16% above the laboratory level. The fact that the bioburden in the treated wing continuously decreased with time while that of the untreated wing continuously increased, does indicate that the antimicrobial treatment was very effective in controlling the bioburden.

Table 3. Air Samples (Average cfu/ft3)

Test Interval

Treated Wing

Untreated Wing

Reduction

6 Months

1.36 (48.3)

1.75 (62.1)

22 %

12 months

1.19 (42.0)

2.26 (79.8)

47 %

18 Months

1.16 (40.9)

2.78 (98.1)

58 %

Reference Values: (Microbiology Lab = 1.00 (35.3)) (Vestibule = 6.69 (236.2)) (Outside = 33.37 (1178.0))

Since the total colony count does not differentiate between species of microorganisms, the air samples taken at the end of the study were examined to determine what viable or living fungi and bacteria were present at that time. For the fungi, when compared to the untreated wing, the treated wing contained 63% less bioburden. This was found to be statistically significant at a P-value = 0.0043 using the Mann-Whitney U test of medians. Also, there was no difference in the distribution of predominant genera of viable fungi between the wings. That is, the same percentage distribution of each species was the same in each of the wings even though the absolute numbers of species was less in the treated wing. For bacteria incubated at 350C, the median reduction was only 25% and was found not to be statistically significant. Also, there was a difference in the distribution of the predominant genera on each wing.

Conclusion

To the authors’ knowledge, this study is the first of its kind involving a healthcare setting. The purpose was to see if the total bioburden or level of microorganisms present in a healthcare environment could be reduced through antimicrobial treatment of surfaces and the air. Since the building was new and contained two identical wings, each containing 12500 square feet (1157 m2), it offered the authors a unique opportunity to conduct a controlled ‘real world’ study.

The treatment consisted of using the well known chlorine based antimicrobial agent triclosan, either through the application of existing products or by developing special purpose products. Physical components of the treated wing included permanent and moveable fixtures, medical instruments, furniture, walls, floors, ceilings and air filters. Included were telephones, computers, filing cabinets, sinks, counters, exam tables, doors and hardware etc. Each item in the treated wing had a corresponding control item on the untreated wing that was tested for comparison. A total of 45 items were selected in each wing for testing surface bioburden. There were 10 locations selected for air sampling on each of the two wings.

The results of the 18-month study showed an average of 40% reduction in colony forming units (cfu) for treated surfaces and a 58% reduction of air borne microorganisms. In the case of air sampling, it was interesting to find that the air quality in the treated wing consistently improved, while

that of the untreated wing got progressively worse. The antimicrobial treatment enabled the wing to maintain the level of airborne bioburden to within 16% of that found in the microbiology lab.

Unfortunately, this study cannot be used to determine what effect the triclosan-treated reusable air filters may have had on reducing the airborne bioburden within the treated wing since the triclosan – treated filters were installed at the same time as the other surfaces were treated. Although the authors realized this at the beginning of the study, there was insufficient time and resources to conduct a comparison of the effect of different treatment applications.

During the study period both wings were used for the same type of outpatient care. This was important to the validity of the study, since dissimilar use functions could have affected the test results and negated a direct comparison. Also, since hospital employees conducted all building maintenance and antimicrobial treatment, strict supervision and proper implementation of specific protocols for cleaning and treating was made possible.

The study had to be terminated after the 18-month period, since after one year of occupancy, renovations and functional changes were being scheduled by management. These resulted in the wings being used for very different types of patient care. Also, to reduce operating costs, all maintenance for the building was contracted out and this prevented any further study to be conducted.

What impact this type of environmental treatment could have on the reduction of nosocomial infections in more critical care facilities remains to be seen. The cost of environmental treatment would have to be determined and compared against any reductions in nosocomial infection rates. However, similar treatment approaches could be integrated into infection control activities and studied within a hospital setting. If nothing else, the building and the patient environment could be maintained in a ‘cleaner’ state of preparedness. Additional comparison of personnel absenteeism rates before and after treatment might also prove interesting, in light of the increasing evidence of the effects of ‘sick building syndromes.’

Obviously, as is the case with many studies like the one reported here, more questions can be asked than answers provided. However, the science is here, the products are available, and nosocomial infections are on the increase. Perhaps it is time to consider improving the treatment of the healthcare environment as well as that of the patient.

Dedication

This paper is dedicated to the memory of Robert S. Watterson III, formerly Vice President of Sales, Microban Products Company, Huntersville NC whose dream was to see the construction of cleaner buildings based on the application of ‘anitmicrobial treated building products’. Perhaps the results of this study suggest that dreams can come true.

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Results and Discussion

Surface Samples

A review of biological swab tests for touch and building surfaces in both wings, showed a consistent reduction of colony forming units (cfu) within the treated wing throughout the test period. The range of reductions and the average for each type of surface tested are summarized in Table 1. It is apparent that surfaces that were touched more frequently had greater reduction in the bioburden. This supports earlier tests by others (Medlin, 1997) who reported that triclosan exhibits increased effectiveness when continuously challenged. This was more clearly demonstrated in the present study in a separate set of tests involving items like telephone handsets and computers. These tests were conducted over a six – month period only. Three different telephones and computers located in the control wing were selected for separate study toward the end of the main study. These were treated with a surface spray containing triclosan. The average reductions in bioburden are presented in Table 2 for the 7-day and 6- month test periods. The effect of repeated handling of these devices resulted in an increase in antimicrobial activity. This lead to a greater reduction in surface bioburden as compared to surfaces that were not touched as frequently, such as walls, floors and ceilings as reported in Table 1.

Table 1. Reduction in cfu on Surfaces in Treated Wing

Surface Treated Test Items (number of sites tested)

Range of Reductions in cfu Compared to Control Wing

Average Reduction in cfu Compared to Control Wing

Fixtures and Components (15)

25 to 91 %

55 %

Medical Instruments (10)

0 to 80 %

45 %

Furniture (5)

0 to 85 %

50 %

Wall Paint (5)

10 to 50 %

25 %

Floor tile (5)

30 to 55 %

40 %

Ceiling tile (5)

15 to 35 %

20 %

Total (45)

0 to 91 %

40 %

Table 2. Reduction in cfu on Telephone and Computer Surfaces

Surface Treated Test Items (number of sites tested)

Seven Days Post-Treatment Ave. Reduction in cfu

Six Months Post-Treatment Ave. Reduction in cfu

Telephone Handsets (3)

55 %

99 %

Computer Keyboards (3)

45 %

85 %

Computer Mice (3)

51 %

82 %

Testing Procedures

Standard microbiological swab and air samples were taken throughout both wings. These tests were scheduled on a rotating basis so that each item and location tested on the treated wing had a corresponding test site on the control wing. Both tests were conducted on the same day and as close as possible in time. Over the 18-month test period, each site was tested approximately every two weeks. There were 45 surface and 10 air sites sampled on each wing, for a total of 110 data point locations. Each week, specific sites were tested. These were rotated on a two-week schedule throughout the 18- month test period.

Surface samples were taken using standard microbiological swabs, covering four square inches (2581 mm2) and using standard culturing protocols. The results were reported in terms of the total number of colony forming units (cfu) of microorganisms appearing on the agar plates following the incubation period. Air samples were taken using a standard Anderson air sampler. These results were recorded in cfu per cubic foot of air sampled. Although each site on each wing was monitored over the entire test period, only average values for all sites within a wing, for any one period, were used for comparison. For example, at six months the average of the 10 air samples taken in the treated wing at that time, were averaged and compared to the average of the corresponding 10 sites in the control wing. This provided a single value that represented the entire wing, even though the distribution of values within the wing may differ somewhat from month to month. The same comparison of average values was made for the surface swab tests.

Treatment

Since the main object of the study was to see what effect the treatment of an entire environment would have on the total bioburden, it was imperative to treat all surfaces including the floors, ceilings, walls, doors, all touch hardware, air filters and all fixtures. The fixtures included sinks, counter tops, examination tables, medical instruments, desks, telephone handsets, computers, filing cabinets, chairs, tables and touch hardware etc. Where possible, existing commercial antimicrobial products were used. For some applications (such as floor wax, protective carpet underlay fabric and paint), special products were developed. No treatment was made to any item within the control wing.

The Building

The skeletal structure of the building was that of a two storied, standard steel beam system with open web steel joists, erected on reinforced concrete foundation walls and footings. The building envelope consisted of brick veneer with the interior consisting of metal studded partitions with drywall. All concrete floors were concrete slab, either on fill or suspended on metal decking. The building was constructed on a sloped site with the second level serving as the front of the building and providing a ground level main entrance. This level had two identical wings that flanked the main entrance of the building, each with 12500 square feet (1157 m2) of floor space. In addition to hallways and restrooms, each wing contained patient waiting and exam rooms, faculty and medical resident offices, as well as nursing and administration areas. Since the building had two wings with identical layouts, each being used for identical outpatient care, it provided a unique opportunity to conduct a controlled study. The lower level housed the labs and support services with exit at the rear of the building. The HVAC system consisted of four main areas. The lower level was served by two separate but equally sized AHUs, each rated at 10,000 CFM. The upper level was served by two equally sized but separate units, each rated at 14,000 CFM. All units were balanced, and had separate outside air intake zones. The building was completed in December 1997 and opened on schedule in January 1998. All antimicrobial treatment of the test wing was completed before the building was opened for occupancy.

Antimicrobial Agent – Triclosan

Triclosan is a diphenyl ether (5-chloro-2-[2,4-dichlorophenoxyl] phenol) and like other chlorine-based chemicals, it acts as a cell wall penetrant. It disrupts the microbial cell wall, disturbing the metabolic process, leading to the death of the organism. Although McMurray et al. (1998) suggest that some organisms may be insensitive to triclosan and could result in the development of resistant strains of organisms, considerable counter evidence and scientific argument dispels this position (FDA 1997, CSMA 1998, Jones 1999). The latter references indicate that currently used antimicrobial agents like triclosan, have very different action mechanisms than antibiotics. Additional studies also indicate that there is no existing clinical evidence to suggest that these agents, as used in ‘real world’ applications, are either mutagenic or prone to create resistive strains of organisms (Russell 2002, McBain et. al. 2002, Fraise 2002). An extensive review of the literature on bacterial resistance to topical antimicrobial products by Jones (1999), clearly indicates that there is no scientific evidence that triclosan has an influence on the development of resistive strains of organisms. Indeed, Jones et al. (2000) verifies that triclosan was clinically effective in reducing MRSA isolates from surgical wounds as well as reducing the percentage of ciprofloxacin-resistant MRSA strains.

It is worthy to note that triclosoan can be incorporated into the voids of any polymeric structure (Medlin 1997), as well as being suspended in certain liquid compounds. Such potential use of an antimicrobial agent makes it attractive for sustained treatment. This was one of the underlying motivations for using it in the present study. The concept was to have all construction materials, fixtures, medical instruments, and contents within the healthcare delivery areas, either surface treated or constructed with an antimicrobial agent as an integral part of the product. A limited number of polymer products containing triclosan were available for this study. The goal was to test these and where necessary, to develop others. These included surface sprays and coating liquids.

Over a period of three years, the authors used various triclosan-treated products and applied them to different problem areas throughout the main campus. These included concrete floor surfaces in the decontamination and food services areas; carpet underlay in maternity areas where spills created obnoxious odors and in shower areas where dampness led to continuous growth of microorganisms and degradation of carpet backing; in bathrooms on toilet seats, sanitary napkin dispensers, sinks and faucets and waste baskets; on counters, floors and isolettes in the Neonatal Intensive Care Unit; and on floor drain covers and mortar joints on bathroom floors and walls. In every application studied, the use of triclosan-treated items resulted in a reduction of surface bioburden.

With the success of these preliminary ‘real world’ tests, the authors began planning for a larger application of the treatment. During this planning period, management decided to construct a new outpatient facility, consisting of two floors, each containing 25,000 square feet (2315 m2) of floor space. This building provided an excellent site for the expanded project. It was scheduled to open in January 1998, at which time this study began.

The Need for Added Protection

With this background and the projection of increased nosocomial infection rates, the question of how to keep the healthcare environment cleaner, and in a more sustainable state of readiness, lead the authors to be challenged beyond simply improving the current cleaning methods. The principal motivation was to provide methods of additional control of the bioburden within a healthcare environment, beyond the regularly scheduled maintenance and cleaning protocols. The idea of providing treatment of the physical environment that would be sustaining and perhaps bridge the periods of use between regular cleaning periods, was worthy of study. The search for various antimicrobial agents that would lend themselves to environmental treatment, led the authors to the use of triclosan, the agent mentioned above. When the authors began the preliminary studies in 1995, a limited number of products containing triclosan were available for application. However, no information existed beyond laboratory findings, that triclosan could control ‘real world’ bioburden, to the degree needed in a healthcare environment.