you can use checks in blade within the double braces like this and add additional classes according to variable values.
<div class="navbar-collapse collapse">
<ul class="nav navbar-nav">
<li>
<a class='home'>{{ HTML::linkRoute('hvertime','Forside') }}</a>
</li>
<li class='{{ ($aktiv == 'hvertredjetime') ? 'active' : '' }}'>
<a class='home'>{{HTML::linkRoute('hvertredjetime','Måling')}}</a>
</li>
...
</ul>
</div>
also see http://www.php.net/manual/en/language.operators.comparison.php for the ternary operators.